BaseTools/PatchCheck: Ignore blank lines in diff

BaseTools/PatchCheck: Ignore blank lines in diff

https://bugzilla.tianocore.org/show_bug.cgi?id=2044

When fixes are made for incorrect line endings, there
are cases where the diff contains blank lines.  Ignore
these blank lines.

Cc: Bob Feng <bob.c.feng@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Bob Feng <bob.c.feng@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>