Fix the operator != on ZString.

testing/zstring_test.cpp

@@ -3,6 +3,13 @@
 
 int main(int argc, char **argv) {
 
+   // Test comparison operations.
+
+   coreutils::ZString test1("");
+   std::cout << (test1 != ".");
+   
+   // Test split operations.
+   
    coreutils::ZString test("11111:22222:33333:44444");
    std::cout << "test pre-split: [" << test << "]." << std::endl;