[subset] limit the max codepoint value to the unicode limit.

When collecting all codepoints in the cmap avoid using large amount of memory for fonts that declare coverage over all 32 bit integers.

src/hb-ot-cmap-table.hh

@@ -37,6 +37,9 @@
  */
 #define HB_OT_TAG_cmap HB_TAG('c','m','a','p')
 
+#ifndef HB_MAX_UNICODE_CODEPOINT_VALUE
+#define HB_MAX_UNICODE_CODEPOINT_VALUE 0x10FFFF
+#endif
 
 namespace OT {
 
@@ -437,8 +440,10 @@ struct CmapSubtableLongSegmented
   {
     for (unsigned int i = 0; i < this->groups.len; i++) {
       hb_set_add_range (out,
-			this->groups[i].startCharCode,
-			this->groups[i].endCharCode);
+			MIN ((unsigned int) this->groups[i].startCharCode,
+			     (unsigned int) HB_MAX_UNICODE_CODEPOINT_VALUE),
+			MIN ((unsigned int) this->groups[i].endCharCode,
+			     (unsigned int) HB_MAX_UNICODE_CODEPOINT_VALUE));
     }
   }