Workaround warning: ‘locale’ is used uninitialized in this function [-Wuninitialized]

'locale' being an uninitialized pointer, I don't believe setting it to nil will
make things worse here.

Tests/Unit/TestSBJsonParser.m

@@ -91,6 +91,7 @@
   test ([obtained compare: expected] == NSOrderedSame);
 #endif
 
+  locale = nil;
   result = [parser objectWithString: @"[ -312.3456 ]"];
   obtained = [result objectAtIndex: 0];
   expected = [NSDecimalNumber decimalNumberWithString: @"-312.3456" locale: locale];