CodeAssist: Ensure perfect match for keywords

...as otherwise the completion windows stays open and gets in the way.

Fixes: QTCREATORBUG-21767
Change-Id: Ib0a841b9d9de52109439f067c466478744361814
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/texteditor/codeassist/genericproposalmodel.cpp

@@ -214,8 +214,13 @@ bool GenericProposalModel::isPerfectMatch(const QString &prefix) const
         if (match == PerfectMatchType::StartsWith)
             return false;
 
-        if (!hasFullMatch && match == PerfectMatchType::Full)
-            hasFullMatch = true;
+        if (match == PerfectMatchType::Full) {
+            if (proposalItem(i)->isKeyword())
+                return true;
+
+            if (!hasFullMatch)
+                hasFullMatch = true;
+        }
     }
 
     return hasFullMatch;