plug-ins: Fix PSP vulnerability (ZDI-CAN-22097)

Resolves #10071.

When reading RLE compressed data, a buffer was allocated to 127 bytes.
However, it can potentially be used to read 128 bytes, leading to a
off-by-one vulnerability. This patch allocates 128 bytes to the buffer
to prevent this from occurring.

plug-ins/common/file-psp.c

@@ -1649,7 +1649,7 @@ read_channel_data (FILE        *f,
         else
           endq = q + line_width * height;
 
-        buf = g_malloc (127);
+        buf = g_malloc (128);
         while (q < endq)
           {
             fread (&runcount, 1, 1, f);