If qemu-kvm quit without saving bitmaps in image(coredump or panic on host),
bitmaps in image can not be used safely anymore, and can not be removed
also. Useless bitmaps should be removed.

Signed-off-by: yaoxu <yaoxu@didichuxing.com>
---
diff --git a/blockdev.c b/blockdev.c
index 58d7570932..c85056a74b 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -2837,31 +2837,35 @@ void qmp_block_dirty_bitmap_remove(const char *node, const char *name,
     Error *local_err = NULL;
 
     bitmap = block_dirty_bitmap_lookup(node, name, &bs, errp);
-    if (!bitmap || !bs) {
+    if (!bs) {
         return;
     }
 
-    if (bdrv_dirty_bitmap_frozen(bitmap)) {
-        error_setg(errp,
-                   "Bitmap '%s' is currently frozen and cannot be removed",
-                   name);
-        return;
-    } else if (bdrv_dirty_bitmap_qmp_locked(bitmap)) {
-        error_setg(errp,
-                   "Bitmap '%s' is currently locked and cannot be removed",
-                   name);
+    if (bitmap) {
+        if (bdrv_dirty_bitmap_frozen(bitmap)) {
+            error_setg(errp,
+                       "Bitmap '%s' is currently frozen and cannot be removed",
+                       name);
+            return;
+        } else if (bdrv_dirty_bitmap_qmp_locked(bitmap)) {
+            error_setg(errp,
+                       "Bitmap '%s' is currently locked and cannot be removed",
+                       name);
+            return;
+        }
+    }
+
+    bdrv_remove_persistent_dirty_bitmap(bs, name, &local_err);
+    if (local_err != NULL) {
+        error_propagate(errp, local_err);
         return;
     }
 
-    if (bdrv_dirty_bitmap_get_persistance(bitmap)) {
-        bdrv_remove_persistent_dirty_bitmap(bs, name, &local_err);
-        if (local_err != NULL) {
-            error_propagate(errp, local_err);
-            return;
-        }
+    if (bitmap) {
+        bdrv_release_dirty_bitmap(bs, bitmap);
     }
 
-    bdrv_release_dirty_bitmap(bs, bitmap);
+    *errp = NULL;
 }
 
 /**