Add an assert that there are less than 2^16 unique strings in a column

Author: TomHodson

src/odc/codec/CodecOptimizer.h

@@ -94,13 +94,14 @@ int CodecOptimizer::setOptimalCodecs(core::MetaData& columns)
             case api::STRING:
 				{
                     n = col.coder().numStrings();
-                                        if (n == 1 && col.coder().dataSizeDoubles() == 1)
+                    ASSERT(n < 65536);
+                    if (n == 1 && col.coder().dataSizeDoubles() == 1) {
 						codec = "constant_string";
-					else if(n < 256)
+                    } else if(n < 256) {
 						codec = "int8_string";
-					else if(n < 65536)
+					} else {
 						codec = "int16_string";
-
+                    }
 
                     std::unique_ptr<core::Codec> newCodec = core::CodecFactory::instance().build<ByteOrder>(codec, col.type());
                     if (codec == "constant_string") {