* rocDecode: Added several fixes to samples. (#668)

- Fixed the build error with videodecodepicfiles sample.
 - Added error handling of sample app command option combination of memory type OUT_SURFACE_MEM_NOT_MAPPED and MD5 generation.

utils/rocvideodecode/roc_video_dec.cpp

@@ -956,7 +956,11 @@ void RocVideoDecoder::SaveFrameToFile(std::string output_file_name, void *surf_m
     } else
         hst_ptr = static_cast<uint8_t *> (surf_mem);
 
-    
+    if (hst_ptr == nullptr) {
+        ROCDEC_ERR("Null surface pointer.");
+        return;
+    }
+
     if (current_output_filename.empty()) {
         current_output_filename = output_file_name;
     }