[coretext] Adjust font size check for 0

src/hb-coretext.cc

diff --git a/src/hb-coretext.cc b/src/hb-coretext.cc
index f43abb9..8cfec1e 100644
--- a/src/hb-coretext.cc
+++ b/src/hb-coretext.cc
@@ -73,7 +73,7 @@
 HB_SHAPER_DATA_ENSURE_DEFINE(coretext, face)
 HB_SHAPER_DATA_ENSURE_DEFINE_WITH_CONDITION(coretext, font,
                                             abs (CTFontGetSize((CTFontRef) data) -
-                                                 (font->ptem < 0 ? HB_CORETEXT_FONT_SIZE : font->ptem)) < 1)
+                                                 (font->ptem <= 0 ? HB_CORETEXT_FONT_SIZE : font->ptem)) < 1)
 
 /*
  * shaper face data
@@ -246,7 +246,7 @@
   if (unlikely (!hb_coretext_shaper_face_data_ensure (face))) return NULL;
   CGFontRef cg_font = (CGFontRef) HB_SHAPER_DATA_GET (face);
 
-  float ptem = font->ptem < 0 ? HB_CORETEXT_FONT_SIZE : font->ptem;
+  float ptem = font->ptem <= 0 ? HB_CORETEXT_FONT_SIZE : font->ptem;
 
   CTFontRef ct_font = create_ct_font (cg_font, ptem);