[HIVE] Validate field extraction

Double check JSON input (which has a different schema)

Relates #259

(cherry picked from commit e479bc2)

hive/src/main/java/org/elasticsearch/hadoop/hive/HiveFieldExtractor.java

@@ -65,7 +65,7 @@ public void processField(Settings settings, String fl) {
         // replace column name with _colX (which is what Hive uses during serialization)
         fieldName = columnNames.get(getFieldName().toLowerCase(Locale.ENGLISH));
 
-        if (!StringUtils.hasText(fieldName)) {
+        if (!settings.getInputAsJson() && !StringUtils.hasText(fieldName)) {
             throw new EsHadoopIllegalArgumentException(
                     String.format(
                             "Cannot find field [%s] in mapping %s ; maybe a value was specified without '<','>' or there is a typo?",