rendering limits in ft_glyphslot_preset_bitmap

I've run into a font that exceeds the limits in
ft_glyphslot_preset_bitmap. Specifically, I'm getting:

[objs:3]      ft_glyphslot_preset_bitmap: [-29 -10 505 202]

with ppem = 50, i.e., 534 > 10 * 50.

This is a completely valid CID CFF font, but it's kind of weird. It's
from a PDF file that appears to have been created by some sort of OCR
process that segmented the scanned image into characters and then
vectorized them (!?). The issue comes up where it converted a
hand-written signature into a single very wide character.

I've checked my analysis by making this change (I'm NOT suggesting
this as a fix - just a confirmation that my analysis is correct):

--- a/src/base/ftobjs.c
+++ b/src/base/ftobjs.c
@@ -503,8 +503,8 @@
                    pbox.xMin < -0x1000000 || pbox.xMax >= 0x1000000 ||
                    pbox.yMin < -0x1000000 || pbox.yMax >= 0x1000000 ||
              ( slot->face                                         &&
-               ( width  > 10 * slot->face->size->metrics.x_ppem ||
-                 height > 10 * slot->face->size->metrics.y_ppem ) ) );
+               ( width  > 11 * slot->face->size->metrics.x_ppem ||
+                 height > 11 * slot->face->size->metrics.y_ppem ) ) );
 
     if ( ret )
       FT_TRACE3(( "ft_glyphslot_preset_bitmap: [%ld %ld %ld %ld]\n",

I'll see if I can get permission from my customer to share the PDF file
and font, if that would be useful.

I'm not sure if it would make sense to increase those limits (to
what?), or if maybe there's some other approach?

- Derek