evas_filter: Add null check for instruction

Summary:
Add a null check for cases where the param passed
from the filter instruction can be a null pointer.

Test Plan: N/A

Reviewers: kimcinoo, Hermet

Subscribers: #reviewers, #committers, cedric

Tags: #efl

Differential Revision: https://phab.enlightenment.org/D12084

src/lib/evas/filters/evas_filter_parser.c

@@ -3436,7 +3436,7 @@ _instr2cmd_transform(Evas_Filter_Context *ctx,
    INSTR_PARAM_CHECK(src);
    INSTR_PARAM_CHECK(dst);
 
-   if (!strcasecmp(op, "vflip"))
+   if (op && !strcasecmp(op, "vflip"))
      flags = EVAS_FILTER_TRANSFORM_VFLIP;
    else
      {