https://src.fedoraproject.org/rpms/mscgen/blob/rawhide/f/mscgen-0.20-width-never-less-than-zero.patch

Description: don't make width < 0 with an off-by-one fix-up
 gdoTextWidth() tries to correct an off-by-one error in the calculated width
 of a text bounding box; but doesn't account for the possibility that the
 bounding box has a size of zero (which is the case in latest libgd for
 zero-width text).  Account for this so we aren't accidentally returning
 -1 where we mean 0.
Author: Steve Langasek <steve.langasek@ubuntu.com>
Bug-Debian: https://bugs.debian.org/960405
Last-Update: 2020-05-15

--- a/src/gd_out.c
+++ b/src/gd_out.c
@@ -212,7 +212,7 @@
      *  the right of the last character for the fixed width
      *  font.
      */
-    return rect[2] - 1;
+    return rect[2] ? rect[2] - 1 : 0;
 #endif
 }