linux PIString fix

libs/main/core/pistring.cpp

@@ -246,7 +246,7 @@ void PIString::appendFromChars(const char * c, int s, const char * codepage) {
 	size_t len = mbsrtowcs(NULL, pc, 0, &state);
 	wchar_t wstr[len+1];
 	mbsrtowcs(&wstr[0], pc, len+1, &state);
-	if (s > 0) free(c_);
+	if (c_) free(c_);
 	enlarge(len);
 	for (size_t i=0; i<len; ++i) (*this)[old_sz+i] = wstr[i];
 //	//qDebug() << "FromChars done" << size();