Do not create patch if there are binary files

"git diff" can accept --binary, which will produce diff with binary content. But patch does not understood
such diff, so we are doomed. Diff with binary file will produce
```
Binary files /dev/null and b/app/assets/images/false.png differ
diff --git a/app/assets/images/foreman.png b/app/assets/images/foreman.png
new file mode 100644
index 0000000..8815824
```
And patch will accept such syntax but will not create the file. Not even empty one.
So this result in silently throwing away some changes.