NULL check environ before dereference

On UNIX, `clearenv` sets `environ` to NULL.
So, NULL is a valid value for `environ`.

Signed-off-by: Dušan Veljko <[email protected]>

Author: dusan-exostellar

rocclr/utils/flags.cpp

@@ -119,11 +119,11 @@ bool Flag::init() {
 #else  // !_WIN32
 #ifdef __APPLE__
   char** environ = *_NSGetEnviron();
+#endif  // __APPLE__
+
   if (environ == NULL) {
     return false;
   }
-#endif  // __APPLE__
-
   for (const char** p = const_cast<const char**>(environ); *p != NULL; ++p) {
     std::string var = *p;
     size_t pos = var.find('=');