Restore symbol names from cache

When reading earlier reported errors from the cache file the symbol names are not handled. This causes suppressions to no longer match when rerunning cppcheck.

lib/errorlogger.cpp

@@ -220,6 +220,8 @@ ErrorMessage::ErrorMessage(const tinyxml2::XMLElement * const errmsg)
             const int line = strline ? std::atoi(strline) : 0;
             const int column = strcolumn ? std::atoi(strcolumn) : 0;
             callStack.emplace_front(file, info, line, column);
+        } else if (std::strcmp(e->Name(),"symbol")==0) {
+            mSymbolNames += e->GetText();
         }
     }
 }