common: Add missing va_end (ggerganov#11529)

The va_copy man page states that va_end must be called to revert
whatever the copy did. For some implementaions, not calling va_end
has no consequences. For others it could leak memory.

common/log.cpp

@@ -206,6 +206,7 @@ struct common_log {
                 vsnprintf(entry.msg.data(), entry.msg.size(), ss.str().c_str(), args_copy);
             }
 #endif
+            va_end(args_copy);
         }
 
         entry.level = level;