coverity#1241372 Negative array index read

Change-Id: I73bae29c6cc737d341381c010face6b587b31598

i18npool/source/nativenumber/nativenumbersupplier.cxx

@@ -611,9 +611,19 @@ sal_Unicode SAL_CALL NativeNumberSupplierService::getNativeNumberChar( const sal
                     return j;
         return inChar;
     }
-    else if (isNumber(inChar) && isValidNatNum(rLocale, nNativeNumberMode)) {
+
+    if (!isNumber(inChar))
+        return inChar;
+
+    if (!isValidNatNum(rLocale, nNativeNumberMode))
+        return inChar;
+
     sal_Int16 langnum = getLanguageNumber(rLocale);
-        switch (nNativeNumberMode) {
+    if (langnum == -1)
+        return inChar;
+
+    switch (nNativeNumberMode)
+    {
         case NativeNumberMode::NATNUM1: // Char, Lower
         case NativeNumberMode::NATNUM4: // Text, Lower, Long
         case NativeNumberMode::NATNUM7: // Text. Lower, Short
@@ -632,7 +642,7 @@ sal_Unicode SAL_CALL NativeNumberSupplierService::getNativeNumberChar( const sal
         default:
             break;
     }
-    }
+
     return inChar;
 }