avfilter/drawtext: make command processing error-resilient

Prevents crash or interruption in text rendering
if new option string contains invalid values.

libavfilter/vf_drawtext.c

@@ -862,20 +862,49 @@ static int config_input(AVFilterLink *inlink)
 
 static int command(AVFilterContext *ctx, const char *cmd, const char *arg, char *res, int res_len, int flags)
 {
-    DrawTextContext *s = ctx->priv;
+    DrawTextContext *old = ctx->priv;
+    DrawTextContext *new = NULL;
+    int ret;
 
     if (!strcmp(cmd, "reinit")) {
-        int ret;
+        new = av_mallocz(sizeof(DrawTextContext));
+        if (!new)
+            return AVERROR(ENOMEM);
+
+        new->class = &drawtext_class;
+        ret = av_opt_copy(new, old);
+        if (ret < 0)
+            goto fail;
+
+        ctx->priv = new;
+        ret = av_set_options_string(ctx, arg, "=", ":");
+        if (ret < 0) {
+            ctx->priv = old;
+            goto fail;
+        }
+
+        ret = init(ctx);
+        if (ret < 0) {
+            uninit(ctx);
+            ctx->priv = old;
+            goto fail;
+        }
+
+        new->reinit = 1;
+
+        ctx->priv = old;
         uninit(ctx);
-        s->reinit = 1;
-        if ((ret = av_set_options_string(ctx, arg, "=", ":")) < 0)
-            return ret;
-        if ((ret = init(ctx)) < 0)
-            return ret;
+        av_freep(old);
+
+        ctx->priv = new;
         return config_input(ctx->inputs[0]);
-    }
+    } else
+        return AVERROR(ENOSYS);
 
-    return AVERROR(ENOSYS);
+fail:
+    av_log(ctx, AV_LOG_ERROR, "Failed to process command. Continuing with existing parameters.\n");
+    av_freep(new);
+    return ret;
 }
 
 static int func_pict_type(AVFilterContext *ctx, AVBPrint *bp,