Describe the bug
UnifiedDiffReader.parseUnifiedDiff throws UnifiedDiffParserException on a patch which apparently looks good:

https://raw.githubusercontent.com/bazelbuild/bazel/master/third_party/aws-sdk-auth-lite/patches-vs-1.11.297/01-bazel-strip-unused.patch

To Reproduce
Run this program:

String patch = new Scanner(new URL(
    "https://raw.githubusercontent.com/bazelbuild/bazel/master/third_party/aws-sdk-auth-lite/patches-vs-1.11.297/01-bazel-strip-unused.patch"
).openStream(), "UTF-8").useDelimiter("\\A").next();

UnifiedDiffReader.parseUnifiedDiff(new StringBufferInputStream(patch));

Expected behavior

No Exceptions.

Actual behavior

Dec 14, 2020 9:49:46 PM com.github.difflib.unifieddiff.UnifiedDiffReader processLine
WARNING: >>> no rule matched \ No newline at end of file
Exception in thread "main" com.github.difflib.unifieddiff.UnifiedDiffParserException: expected file start line not found
at com.github.difflib.unifieddiff.UnifiedDiffReader.parse(UnifiedDiffReader.java:95)
at com.github.difflib.unifieddiff.UnifiedDiffReader.parseUnifiedDiff(UnifiedDiffReader.java:146)
...

System

• Java version: openjdk-11
• Version: 4.9

Notes

👋 java-diff-utils maintainers again! Here is another corner case I found. The patch comes from the Bazel project, so once again it's OK to include in tests.