Initiialze character set only once.

Author: blach

Core/Source/NSString+DTLocalizableStringScanner.m

@@ -200,7 +200,12 @@ - (NSString *)stringByDecodingUnicodeSequences
 {
     NSUInteger length = [self length];
 
-    NSCharacterSet *hex = [NSCharacterSet characterSetWithCharactersInString:@"0123456789abcdefABCDEF"];
+    static NSCharacterSet *hex = nil;
+    
+    static dispatch_once_t onceToken;
+    dispatch_once(&onceToken, ^{
+        hex = [NSCharacterSet characterSetWithCharactersInString:@"0123456789abcdefABCDEF"];
+    });
 
     unichar *characters = calloc(length, sizeof(unichar));