fix: move ownership of line to oldline

- set line to null when moved
- also, free line when loading from history

src/msh.c

@@ -357,6 +357,7 @@ int main(int argc, char** argv) {
                             }
 
                             oldline = line;
+                            line = NULL;
                         }
                     } else if (ansi == ANSI_CURSOR_DOWN && historyoffset > 0) {
                         historyoffset--;
@@ -383,6 +384,11 @@ int main(int argc, char** argv) {
                     if (load_from_hist == 1) {
                         char*  historyline = history[historyi - (historyoffset)];
                         size_t historylinelen = strlen(historyline);
+
+                        if (line != NULL) {
+                            free(line);
+                        }
+
                         line = malloc(historylinelen + 1);
                         if (line == NULL) {
                             retval = 1;