patch Pango to handle font-info failure

Getting NULL from CTFontCollectionCreateMatchingFontDescriptors()
might indicate a font installation problem; I'm not sure. In any case,
checking for NULL avoids a crash on at least one installation.

racket/src/native-libs/build.rkt

@@ -128,6 +128,9 @@
 ;; Support registration of extra font families:
 (define-runtime-path coretext-fontreg-patch "patches/coretext-fontreg.patch")
 
+;; Avoid crash when CTFontCollectionCreateMatchingFontDescriptors fails:
+(define-runtime-path coretext-nullarray "patches/coretext-nullarray.patch")
+
 ;; Enable "symbol" fonts, and fix off-by-one:
 (define-runtime-path win32text-patch "patches/win32text.patch")
 
@@ -441,6 +444,7 @@
 				      "--with-dynamic-modules=no"))
                        #:patches (list coretext-patch
                                        coretext-fontreg-patch
+                                       coretext-nullarray
                                        win32text-patch))]
     [("gmp") (config #:patches (if gcc-4.0? (list gmp-weak-patch) null)
                      #:configure (append

racket/src/native-libs/patches/coretext-nullarray.patch

@@ -0,0 +1,21 @@
+diff -r -u old/pango-1.36.6/pango/pangocoretext-fontmap.c new/pango-1.36.6/pango/pangocoretext-fontmap.c
+--- old/pango-1.36.6/pango/pangocoretext-fontmap.c	2015-11-07 08:15:41.000000000 -0700
++++ new/pango-1.36.6/pango/pangocoretext-fontmap.c	2015-11-07 08:16:56.000000000 -0700
+@@ -649,7 +649,7 @@
+ 
+       italic_faces = g_hash_table_new (g_direct_hash, g_direct_equal);
+ 
+-      count = CFArrayGetCount (ctfaces);
++      count = (ctfaces ? CFArrayGetCount (ctfaces) : 0);
+       for (i = 0; i < count; i++)
+         {
+           PangoCoreTextFace *face;
+@@ -669,7 +669,7 @@
+ 
+       CFRelease (font_descriptors);
+       CFRelease (attributes);
+-      CFRelease (ctfaces);
++      if (ctfaces) CFRelease (ctfaces);
+ 
+       /* For all fonts for which a non-synthetic italic variant does
+        * not exist on the system, we create synthesized versions here.