[gimp] libgimpbase: return 0 for GIMP_UNIT_PIXEL in gimp_unit_get_factor().

[Jehan <jehanp src gnome org>]

commit f705bfb3957fa20c65e4544fa09b58893eb7d768
Author: Jehan <jehan girinstud io>
Date:   Sat Aug 17 12:07:31 2019 +0200

    libgimpbase: return 0 for GIMP_UNIT_PIXEL in gimp_unit_get_factor().
    
    Just as documented, pixel unit should always return factor 0. There is
    no need to call _gimp_unit_vtable.unit_get_factor().
    
    This is even more important as there is one implementation of
    unit_get_factor() in core, and another in libgimp and the one in libgimp
    is expecting unit to always be >= GIMP_UNIT_INCH. So we were getting
    CRITICALs in libgimp when calling gimp_unit_get_factor() on pixel unit
    (for instance when drawing a GimpRuler).

 libgimpbase/gimpunit.c | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/libgimpbase/gimpunit.c b/libgimpbase/gimpunit.c
index e6f2df2c0b..2184861691 100644
--- a/libgimpbase/gimpunit.c
+++ b/libgimpbase/gimpunit.c
@@ -233,6 +233,9 @@ gimp_unit_get_factor (GimpUnit unit)
 {
   g_return_val_if_fail (_gimp_unit_vtable.unit_get_factor != NULL, 1.0);
 
+  if (unit == GIMP_UNIT_PIXEL)
+    return 0.0;
+
   return _gimp_unit_vtable.unit_get_factor (unit);
 }