doc/examples/qsv_transcode: Simplify str_to_dict() loop

Fixes: CID1517022 Logically dead code

Sponsored-by: Sovereign Tech Fund
Reviewed-by: "Xiang, Haihao" <haihao.xiang@intel.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 191950d1bf)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

doc/examples/qsv_transcode.c

@@ -75,8 +75,7 @@ static int str_to_dict(char* optstr, AVDictionary **opt)
         if (value == NULL)
             return AVERROR(ENAVAIL);
         av_dict_set(opt, key, value, 0);
-    } while(key != NULL);
-    return 0;
+    } while(1);
 }
 
 static int dynamic_set_parameter(AVCodecContext *avctx)