Bug 1614868 - Ignore combining diacritic characters in history search. r=jfkthame,mak

IsCombiningDiacritic(-1) returns false, so there is no need to specially
handle -1 in GetLowerUTF8Codepoint_inline.

It is no longer necessary for GetNaked to check whether a character is a
combining character because all callers now skip combining diacritics
and GetNaked already makes sure that decomposition removes a diacritic
and not something else.

Differential Revision: https://phabricator.services.mozilla.com/D62533

intl/unicharutil/util/nsUnicodeProperties.cpp

@@ -315,6 +315,9 @@ uint32_t GetNaked(uint32_t aCh) {
   static const UNormalizer2* normalizer;
   static HashMap<uint32_t, uint32_t> nakedCharCache;
 
+  NS_ASSERTION(!IsCombiningDiacritic(aCh),
+               "This character needs to be skipped");
+
   HashMap<uint32_t, uint32_t>::Ptr entry = nakedCharCache.lookup(aCh);
   if (entry.found()) {
     return entry->value();
@@ -340,13 +343,6 @@ uint32_t GetNaked(uint32_t aCh) {
     return aCh;
   }
 
-  if (u_getIntPropertyValue(aCh, UCHAR_GENERAL_CATEGORY) & U_GC_M_MASK) {
-    // The character is itself a combining character, and we don't want to use
-    // its decomposition into multiple combining characters.
-    baseChar = aCh;
-    goto cache;
-  }
-
   if (NS_IS_HIGH_SURROGATE(decomposition[0])) {
     baseChar = SURROGATE_TO_UCS4(decomposition[0], decomposition[1]);
     combiners = decomposition + 2;