fix: immediately continue when empty line is read

src/msh.c

@@ -457,12 +457,24 @@ 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);
 
         line[linelen] = 0;
 
+        if (linelen == 0) {
+            free(line);
+            line = NULL;
+            continue;
+        }
+
         fprintf(historyfile, "%s\n", line);
         fflush(historyfile);