fix for fastfloat_strncasecmp for wchar_t and larger char types

Author: dalle

include/fast_float/float_common.h

@@ -222,12 +222,15 @@ fastfloat_really_inline constexpr bool is_supported_char_type() {
 // Compares two ASCII strings in a case insensitive manner.
 template <typename UC>
 inline FASTFLOAT_CONSTEXPR14 bool
-fastfloat_strncasecmp(UC const *input1, UC const *input2, size_t length) {
-  char running_diff{0};
+fastfloat_strncasecmp(UC const *actual_mixedcase, UC const *expected_lowercase,
+                      size_t length) {
   for (size_t i = 0; i < length; ++i) {
-    running_diff |= (char(input1[i]) ^ char(input2[i]));
+    UC const actual = actual_mixedcase[i];
+    if ((actual < 256 ? actual | 32 : actual) != expected_lowercase[i]) {
+      return false;
+    }
   }
-  return (running_diff == 0) || (running_diff == 32);
+  return true;
 }
 
 #ifndef FLT_EVAL_METHOD