Match table exhaustively for ConvertToDelta to avoid scala.MatchError (delta-io#3411)

## Description
Make the match loop exhaustive to avoid scala.MatchError

## How was this patch tested?
Existing Unit tests.

Author: mingdai-db

spark/src/main/scala/org/apache/spark/sql/delta/commands/ConvertToDeltaCommand.scala

@@ -133,6 +133,10 @@ abstract class ConvertToDeltaCommandBase(
         case _: DeltaTableV2 =>
           // Already a Delta table
           None
+        case other =>
+          throw DeltaErrors.operationNotSupportedException(
+            s"Converting an unsupported table type $other to a Delta table",
+            tableIdentifier)
       }
     } else {
       Some(ConvertTarget(