cmd: Fix potential memory leak

Signed-off-by: Pavel Borzenkov <pavel.borzenkov@gmail.com>
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>

cmd.c

@@ -329,16 +329,21 @@ char **breakline(char *input, int *count)
     int c = 0;
     char *p;
     char **rval = calloc(sizeof(char *), 1);
+    char **tmp;
 
     while (rval && (p = qemu_strsep(&input, " ")) != NULL) {
         if (!*p) {
             continue;
         }
         c++;
-        rval = realloc(rval, sizeof(*rval) * (c + 1));
-        if (!rval) {
+        tmp = realloc(rval, sizeof(*rval) * (c + 1));
+        if (!tmp) {
+            free(rval);
+            rval = NULL;
             c = 0;
             break;
+        } else {
+            rval = tmp;
         }
         rval[c - 1] = p;
         rval[c] = NULL;