Fix handling of unsigned char strings (#373)

fmt/format.h

@@ -1277,7 +1277,9 @@ class MakeValue : public Arg {
 
   FMT_MAKE_VALUE(char *, string.value, CSTRING)
   FMT_MAKE_VALUE(const char *, string.value, CSTRING)
+  FMT_MAKE_VALUE(signed char *, sstring.value, CSTRING)
   FMT_MAKE_VALUE(const signed char *, sstring.value, CSTRING)
+  FMT_MAKE_VALUE(unsigned char *, ustring.value, CSTRING)
   FMT_MAKE_VALUE(const unsigned char *, ustring.value, CSTRING)
   FMT_MAKE_STR_VALUE(const std::string &, STRING)
   FMT_MAKE_STR_VALUE(StringRef, STRING)

test/format-test.cc

@@ -1343,6 +1343,8 @@ TEST(FormatterTest, FormatUCharString) {
   EXPECT_EQ("test", format("{0:s}", str));
   const unsigned char *const_str = str;
   EXPECT_EQ("test", format("{0:s}", const_str));
+  unsigned char *ptr = str;
+  EXPECT_EQ("test", format("{0:s}", ptr));
 }
 
 TEST(FormatterTest, FormatPointer) {