Patch() misreports paths containing " b/" and throws for the whole repo when any file name is C-quoted by git #120

What's wrong

GitPatchParser.ReadPathFromFileStart (GitIntegration/Parsing/GitPatchParser.cs:~191-206) finds the new-side path in a diff --git a/X b/Y header by taking whatever follows the last " b/". That fails in two ways.

1. Wrong path when the name contains b/

If you modify Plan b/notes.txt, git emits:

diff --git a/Plan b/notes.txt b/Plan b/notes.txt

The last b/ is inside the new-side path, so GitFilePatch.Path comes back as notes.txt. The code comment says searching from the end protects against the old side containing b/. It doesn't, because without a rename the new side is the same text as the old side.

The patch is silently attributed to the wrong file. A staging UI shows the wrong name, and ForPath(file.Path) or Unstage(file.Path) targets a different file, or none.

2. One quoted name makes the whole call throw

core.quotepath=false only turns off escaping of non-ASCII characters. Git still C-quotes names that contain ", \, a tab or a control character:

diff --git "a/say \"hi\".txt" "b/say \"hi\".txt"

That header has no b/, so Patch() throws GitParseException: A diff header has no recognizable new-side path. One legally named file on Linux or macOS makes the patch for every other file in the repository unreadable. Diff() copes with the same file because it uses -z.

rename from / rename to lines (ApplyHeaderLine, around line 212) are quoted the same way and aren't unquoted either.

Suggested fix

• No rename or copy: the old and new paths are identical. Split a/P b/P at the midpoint and check that both halves match. This is the approach git's own git_header_name takes.
• Otherwise: take the path from the +++ b/… line (stripping the trailing tab git appends when a path contains a space) or from rename to.
• Quoted operands: when an operand starts with ", decode git's C escapes (\", \\, \t, \n, octal \NNN UTF-8 bytes) before building the RelativeFilePath. Do the same for rename from / rename to.
• Add parser fixtures for Plan b/notes.txt and for say "hi".txt.