Remove extra "+ rowNumber"

This was accidentally introduced in
https://skia-review.googlesource.com/13274. That CL replaced

    frameContext->yOffset() + rowNumber + repeatCount

with

    yBegin + rowNumber + repeatCount

(ignoring the static_cast), but yBegin = frameContext->yOffset() +
rowNumber, so this introduced an extra rowNumber. The error is harmless
(yEnd is only compared against yBegin), but this commit makes the line
more correct.

Change-Id: I5a895eae03cbe55f8cf518d57e08c03400385e1f
Reviewed-on: https://skia-review.googlesource.com/c/libgifcodec/+/339830
Commit-Queue: Leon Scroggins <scroggo@google.com>
Commit-Queue: Derek Sollenberger <djsollen@google.com>
Auto-Submit: Leon Scroggins <scroggo@google.com>
Reviewed-by: Derek Sollenberger <djsollen@google.com>

SkLibGifCodec.cpp

diff --git a/SkLibGifCodec.cpp b/SkLibGifCodec.cpp
index d0752ed..71d0e81 100644
--- a/SkLibGifCodec.cpp
+++ b/SkLibGifCodec.cpp
@@ -415,7 +415,7 @@
     const int xBegin = frameContext->xOffset();
     const int yBegin = frameContext->yOffset() + rowNumber;
     const int xEnd = std::min(xBegin + width, this->dimensions().width());
-    const int yEnd = std::min(yBegin + rowNumber + repeatCount, this->dimensions().height());
+    const int yEnd = std::min(yBegin + repeatCount, this->dimensions().height());
     // FIXME: No need to make the checks on width/xBegin/xEnd for every row. We could instead do
     // this once in prepareToDecode.
     if (!width || (xBegin < 0) || (yBegin < 0) || (xEnd <= xBegin) || (yEnd <= yBegin))