Fix double free regression and realloc memleak

libr/core/cmd.c

@@ -2925,7 +2925,6 @@ R_API char *r_core_cmd_str_pipe(RCore *core, const char *cmd) {
 		if (s) {
 			r_file_rm (tmp);
 			r_sandbox_disable (0);
-			free (s);
 			free (tmp);
 			free (_cmd);
 			return s;

libr/util/str.c

@@ -933,10 +933,12 @@ R_API char *r_str_append(char *ptr, const char *string) {
 	}
 	plen = strlen (ptr);
 	slen = strlen (string);
-	ptr = realloc (ptr, slen + plen + 1);
-	if (!ptr) {
+	char *newptr = realloc (ptr, slen + plen + 1);
+	if (!newptr) {
+		free (ptr);
 		return NULL;
 	}
+	ptr = newptr;
 	memcpy (ptr + plen, string, slen + 1);
 	return ptr;
 }