fix: when set, free oldline after reading line

src/msh.c

@@ -457,6 +457,12 @@ int main(int argc, char** argv) {
             fflush(stdout);
         }
 
+        // oldline is only valid while reading
+        if (oldline != NULL) {
+            free(oldline);
+            oldline = NULL;
+        }
+
         putc('\n', stdout);
 
         tcsetattr(fileno(stdin), 0, &orig_term);