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.
