Fix three real bugs found during a full ZString review

operator< computed end2 as valuex.getData() + valuex.getLength() - mixing
an absolute pointer (getData(), the buffer start) with a cursor-relative
length (getLength(), remaining-from-cursor). For any ZString with a
non-zero cursor offset this produces an end pointer short of the true
buffer end by exactly the amount already consumed, truncating the
comparison early. Fixed to use valuex.data + valuex.length (the true
end), matching how end1 was already computed for *this. operator<=,
>=, and > were separately broken (flagged by the codes own TODO
comment) - they compared via strncmp from data (ignoring cursor
entirely), inconsistent with operator< and with each other. Replaced
all three with derivations from the now-correct operator< (a <= b is
!(b < a), etc.) - guarantees trichotomy by construction instead of
three independently-written comparison loops.

substring(start, len): when the requested length overran the buffer,
computed newlen as endChar - end (the overrun amount) instead of
end - startChar (the actual remaining valid length) - backwards, and
stored into a char (max 127), silently wrapping for longer strings.
Fixed the formula and widened to size_t.

trimCRLF(): read *(data + length - 1) unconditionally, including when
length is already 0 - one byte before the buffer on an empty string.
Guarded both checks on length > 0.

Verified: full local compile (identical result to before - 13/20 clean,
same pre-existing StreamReader.h-blocked failures, nothing new broken);
a dedicated runtime test exercising all three fixes plus a trichotomy
check across multiple cursor offsets - all 13 assertions pass. Test
file not included in this commit.

ZString.cpp

@@ -70,11 +70,16 @@ namespace coreutils {
 	free(cdata);      
    }
 
+   // All four relational operators compare from each side's current cursor position to its
+   // own true buffer end (data+length), not from data alone - this class is a cursor/view
+   // over a buffer (see parsed()/unparsed()), so "less than" means "the remaining, unparsed
+   // content compares less than", consistently across <, <=, >=, and >.
+
    bool ZString::operator<(const ZString &valuex) const {
       char *end1 = data + length;
-      char *end2 = valuex.getData() + valuex.getLength();
+      char *end2 = valuex.data + valuex.length;
       char *cursor1 = cursor;
-      char *cursor2 = valuex.getCursor();
+      char *cursor2 = valuex.cursor;
       while((cursor1 < end1) && (cursor2 < end2)) {
 	 if(*cursor1 < *cursor2)
 	   return 1;
@@ -90,18 +95,16 @@ namespace coreutils {
       return 0;
    }
 
-   // TODO: Fix the following comparison operators to handle the length problem appropriately.
-   
    bool ZString::operator<=(const ZString &valuex) const {
-      return (strncmp(data, valuex.data, valuex.length <= length ? valuex.length : length) <= 0);
+      return !(valuex < *this);
    }
 
    bool ZString::operator>=(const ZString &valuex) const {
-      return (strncmp(data, valuex.data, valuex.length <= length ? valuex.length : length) >= 0);
+      return !(*this < valuex);
    }
 
    bool ZString::operator>(const ZString &valuex) const {
-      return (strncmp(data, valuex.data, valuex.length <= length ? valuex.length : length) > 0);
+      return (valuex < *this);
    }
 
    bool ZString::operator==(const ZString valuex) {
@@ -261,7 +264,12 @@ namespace coreutils {
       char *end = data + length;
       char *startChar = data + start;
       char *endChar = startChar + len;
-      char newlen = endChar > end ? endChar - end: len;
+      // Clamp to the remaining valid length (end - startChar) when the requested
+      // length would overrun the buffer - previously computed endChar - end (the
+      // overrun amount itself) instead, handing back a length far past what's
+      // actually there. size_t also fixes a latent overflow for strings > 127
+      // bytes that the old `char newlen` would have silently wrapped.
+      size_t newlen = endChar > end ? (size_t)(end - startChar) : (size_t)len;
       if(startChar < end)
 	return ZString(startChar, newlen);
       return ZString();
@@ -600,9 +608,11 @@ namespace coreutils {
 
    bool ZString::trimCRLF() {
       int len = length;
-      if (*(data + length - 1)  == '\n')
+      // Guard both checks against an empty string - previously read *(data - 1)
+      // (one byte before the buffer) when length was already 0.
+      if ((length > 0) && (*(data + length - 1) == '\n'))
 	--length;
-      if (*(data + length - 1) == '\r')
+      if ((length > 0) && (*(data + length - 1) == '\r'))
 	--length;
       if (cursor >= (data + length))
 	     cursor = data + length;