Fix out-of-bounds read. (#1503)

getLocationLIneAndColumn would read past the end of the provided buffer if generating an error message at the end of the stream, if the final character was `\r`.

Co-authored-by: Jordan Bayles <[email protected]>

Author: vslashg

src/lib_json/json_reader.cpp

@@ -761,7 +761,7 @@ void Reader::getLocationLineAndColumn(Location location, int& line,
   while (current < location && current != end_) {
     Char c = *current++;
     if (c == '\r') {
-      if (*current == '\n')
+      if (current != end_ && *current == '\n')
         ++current;
       lastLineStart = current;
       ++line;
@@ -1801,7 +1801,7 @@ void OurReader::getLocationLineAndColumn(Location location, int& line,
   while (current < location && current != end_) {
     Char c = *current++;
     if (c == '\r') {
-      if (*current == '\n')
+      if (current != end_ && *current == '\n')
         ++current;
       lastLineStart = current;
       ++line;