Handle different number of columns in dummy driver

Number of cols is inferred from the number of fields in the first row.

spec/dummy_driver.cr

@@ -81,6 +81,7 @@ class DummyDriver < DB::Driver
     def initialize(statement, query)
       super(statement)
       @top_values = query.split.map { |r| r.split(',') }.to_a
+      @column_count = @top_values.size > 0 ? @top_values[0].size : 2
 
       @@last_result_set = self
     end
@@ -99,7 +100,7 @@ class DummyDriver < DB::Driver
     end
 
     def column_count
-      2
+      @column_count
     end
 
     def column_name(index)