msys2-runtime: fix diff context

One of the recent patches applies cleanly when cherry-picked, but not
when applied as a patch, because I merged the `msys2-3.4.9` branch whose
patches' context is changed by patches that are in Git for Windows only,
and that are applied before the fixups.

I cherry-picked the last patch manually, generated the diff, and
adjusted the patch. This will have to do for now, if we run
`./update-patches.sh` again before rebasing to a newer MSYS2 runtime
version, we will have to re-apply this here commit.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

msys2-runtime/0063-fixup-Add-functionality-for-converting-UNIX-paths-in.patch

@@ -11,10 +11,10 @@ Don't memchr behind end, it2
  1 file changed, 2 insertions(+), 2 deletions(-)
 
 diff --git a/winsup/cygwin/msys2_path_conv.cc b/winsup/cygwin/msys2_path_conv.cc
-index d4f0192..5c59291 100644
+index 617f74c4b9..133939a7a8 100644
 --- a/winsup/cygwin/msys2_path_conv.cc
 +++ b/winsup/cygwin/msys2_path_conv.cc
-@@ -431,7 +431,7 @@ path_type find_path_start_and_type(const char** src, int recurse, const char* en
+@@ -490,7 +490,7 @@ skip_p2w:
              if (isalpha(ch) && (*(it2+1) == ':') && (*(it2+2) == '/')) {
                  return SIMPLE_WINDOWS_PATH;
              }
@@ -23,12 +23,12 @@ index d4f0192..5c59291 100644
                  *src = it2;
                  return find_path_start_and_type(src, true, end);
              }
-@@ -458,7 +458,7 @@ path_type find_path_start_and_type(const char** src, int recurse, const char* en
-                 } else {
+@@ -519,7 +519,7 @@ skip_p2w:
+                         goto skip_p2w;
                      return POSIX_PATH_LIST;
                  }
 -            } else if (memchr(it2, '=', end - it) == NULL) {
 +            } else if (memchr(it2, '=', end - it2) == NULL) {
                  return SIMPLE_WINDOWS_PATH;
              }
-         }
+         } else if (ch != '.') {