Verify array input to PG::TypeMapByColumn

This could cause a segfault.

Fixes #620

ext/pg_type_map_by_column.c

@@ -54,6 +54,7 @@ pg_tmbc_fit_to_query( VALUE self, VALUE params )
 	t_tmbc *this = RTYPEDDATA_DATA( self );
 	t_typemap *default_tm;
 
+	Check_Type(params, T_ARRAY);
 	nfields = (int)RARRAY_LEN( params );
 	if ( this->nfields != nfields ) {
 		rb_raise( rb_eArgError, "number of result fields (%d) does not match number of mapped columns (%d)",

spec/pg/type_map_by_column_spec.rb

@@ -182,6 +182,12 @@ def decode(res, tuple, field)
 		expect{ PG::TypeMapByColumn.new( [123] ) }.to raise_error(TypeError, /wrong argument type (Integer|Fixnum)/)
 	end
 
+	it "should raise an error for invalid input when used as type_map" do
+		map = PG::TypeMapByColumn.new([PG::TextEncoder::Integer.new])
+		record_encoder = PG::TextEncoder::Record.new(type_map: map)
+		expect{ record_encoder.encode(123) }.to raise_error(TypeError)
+	end
+
 	it "shouldn't allow result mappings with different number of fields" do
 		res = @conn.exec( "SELECT 1" )
 		expect{ res.type_map = PG::TypeMapByColumn.new([]) }.to raise_error(ArgumentError, /mapped columns/)