Fix external/picosat undefined behaviour.

Slightly simplified after discussion with @arrowd.

UndefinedBehaviour.suppress.in

@@ -1,9 +1,6 @@
 #
-# These are errors that need to be taken care of, but in the sprit of
-# "Put Your Own Oxygen Mask on First", we provide here a suppression list for
-# _external_ sources.
+# Suppress errors that are recognized but fix is considered beyond the scope of this project.
+# (e.g. in external source).
 #
-
-# external/picosat/picosat.c:3432:33: runtime error: applying non-zero offset 8 to null pointer
-# +SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior external/picosat/picosat.c:3432:33 
-pointer-overflow:picosat.c
+# For syntax see: https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html#issue-suppression
+#

external/picosat/picosat.c

@@ -3429,7 +3429,8 @@ satisfied (PS * ps)
     return 0;
   assert (!ps->conflict);
   assert (bcp_queue_is_empty (ps));
-  return ps->thead == ps->trail + ps->max_var;	/* all assigned */
+  return (ps->thead == ps->trail && 0 == ps->max_var)
+      || (ps->trail && ps->thead == ps->trail + ps->max_var); /* all assigned */
 }
 
 static void