Fix MString::fromHex() silently swallowing the odd-length-input error

The Exception on the odd-length-input path was constructed but never
thrown (missing throw keyword) - the temporary was destroyed with no
effect, so execution fell through to an out-of-bounds nextChar() read
past the exhausted buffer instead of raising an error. Added the
missing throw.

Verified via full local compile: MString.cpp builds clean standalone;
a full-repo pass shows only the pre-existing, already-known
StreamReader.h-missing failures (7 files, unrelated to this change),
confirmed via each error log individually.

MString.cpp

@@ -390,7 +390,7 @@ namespace coreutils {
 	 ch1 <<= 4;
 	 ch1 &= 240;
 	 if(eod())
-	   coreutils::Exception("conversion from hex requires even number of characters.");
+	   throw coreutils::Exception("conversion from hex requires even number of characters.");
 	 char ch2 = nextChar();
 	 ch2 -= 48;
 	 if(ch2 > 9)