avfilter/crop: avoid premature eval error

Width and height expressions can refer to each other. Width is
evaluated twice to allow for reference to output height. So we
should not error out upon failure of first evaluation of width.

libavfilter/vf_crop.c

@@ -174,10 +174,9 @@ static int config_input(AVFilterLink *link)
         s->vsub = pix_desc->log2_chroma_h;
     }
 
-    if ((ret = av_expr_parse_and_eval(&res, (expr = s->w_expr),
-                                      var_names, s->var_values,
-                                      NULL, NULL, NULL, NULL, NULL, 0, ctx)) < 0)
-        goto fail_expr;
+    av_expr_parse_and_eval(&res, (expr = s->w_expr),
+                           var_names, s->var_values,
+                           NULL, NULL, NULL, NULL, NULL, 0, ctx);
     s->var_values[VAR_OUT_W] = s->var_values[VAR_OW] = res;
     if ((ret = av_expr_parse_and_eval(&res, (expr = s->h_expr),
                                       var_names, s->var_values,