Bug 1577273 - Use strnlen to test if source URLs are too long, r=tcampbell.

Differential Revision: https://phabricator.services.mozilla.com/D43848

--HG--
extra : moz-landing-system : lando

js/src/debugger/Debugger.cpp

@@ -2276,7 +2276,8 @@ static bool RememberSourceURL(JSContext* cx, HandleScript script) {
   }
 
   const char* filename = script->filename();
-  if (!filename || strlen(filename) > SourceURLMaxLength) {
+  if (!filename ||
+      strnlen(filename, SourceURLMaxLength + 1) > SourceURLMaxLength) {
     return true;
   }