Broken parsing for patches with `new file mode 100644`

[janedbal]

When a file contains new files, diff chunks contain a line with patch contents (new file mode 100644), not the actual file contents.

Example patch:

diff --git a/file1.txt b/file1.txt
new file mode 100644
--- /dev/null
+++ b/file1.txt
@@ -0,0 +1,2 @@
+Line A
+Line B
diff --git a/file2.txt b/file2.txt
new file mode 100644
--- /dev/null
+++ b/file2.txt
@@ -0,0 +1,2 @@
+Line X
+Line Y

Reproduced in https://github.com/sebastianbergmann/diff/pull/132