From: Pranav Batra <batrapranav@chromium.org>
  
The hpcups filter increments the green color value of the last pixel on each
row if it matches the previous pixel or seed pixel color value to simplify the
implementation of a run length encoding compression algorithm.

If the seed pixel has color value 0x0000xx, the last pixel 0xffffxx, and the
previous pixel 0xffffxx, then the last pixel's color value will overflow to
0x0000xx, the same as the seed pixel. This will cause an assertion to fail and
the filter to crash.

This patch fixes the bug by incrementing the green color value of the last
pixel if it has a color value less than 0x80 and decrementing if the color
value is greater than 0x80.

https://bugs.launchpad.net/hplip/+bug/1933552

--- a/prnt/hpcups/Mode10.cpp
+++ b/prnt/hpcups/Mode10.cpp
@@ -159,12 +159,13 @@ This function compresses a single row per call.
 
     // Setup sentinal value to replace last pixel of curRow. Simplifies future end condition checking.
     uint32_t realLastPixel = getPixel(curRowPtr, lastPixel);
+    int delta = (realLastPixel & 0xff00U) < 0x8000U ? 0x100 : -0x100;
 
     uint32_t newLastPixel = realLastPixel;
     while ((getPixel (curRowPtr, lastPixel - 1) == newLastPixel) ||
            (getPixel (seedRowPtr, lastPixel) == newLastPixel))
     {
-        putPixel (curRowPtr, lastPixel, newLastPixel += 0x100); // add one to green.
+        putPixel (curRowPtr, lastPixel, newLastPixel += delta); // modify green by one.
     }
     unsigned int curPixel = 0;
     unsigned int seedRowPixelCopyCount;