fixes #439; Avoid indexing an empty array in HaskellNamesValidator

src/com/haskforce/language/HaskellNamesValidator.java

@@ -6,6 +6,7 @@
 import org.jetbrains.annotations.NotNull;
 
 import java.util.Arrays;
+import java.util.regex.Pattern;
 
 /**
  * Ensures names are legal Haskell. Used by refactoring.
@@ -35,15 +36,17 @@ public boolean isKeyword(@NotNull String name, Project project) {
      */
     @Override
     public boolean isIdentifier(@NotNull String name, Project project) {
-        String[] parts = name.split("\\.");
-
+        String[] parts = DOT_REGEX.split(name);
+        if (parts.length == 0) return false;
         for (int i = 0; i < parts.length - 1; i++) {
             String word = parts[i];
             if (!isModid(word, project)) return false;
         }
         return isOneid(parts[parts.length - 1], project, true);
     }
 
+    static Pattern DOT_REGEX = Pattern.compile("\\.");
+
     /**
      * Extended grammar for varid/conid from Haskell 2010 specification. Also allows
      * underscore as start on varids.