plug-ins: Allocate more space for 4bpp TIM textures

Resolves #16052
Per mzfr, the pixel array for 4bpp TIM textures needs to
be allocated twice as large since each byte in the file
stores two pixel indexes when opened.

plug-ins/common/file-tim.c

@@ -524,7 +524,7 @@ load_image (GFile        *file,
 
             for (gint i = 0; i < height; i++)
               {
-                guchar row[width];
+                guchar row[width * 2];
 
                 fread (&pixels, width, 1, fp);