compiler: fix interface bug

vlib/compiler/fn.v

@@ -839,9 +839,15 @@ fn (p mut Parser) fn_call(f mut Fn, method_ph int, receiver_var, receiver_type s
 						idx = i
 					}
 				}
-				p.cgen.resetln('')
 				var := p.expr_var.name
 				iname := f.args[0].typ // Speaker
+				// remove useless var
+				if p.cgen.is_tmp {
+					p.cgen.tmp_line = p.cgen.tmp_line.replace(' $var', '')
+				}
+				else {
+					p.cgen.cur_line = p.cgen.cur_line.replace(' $var', '')
+				}
 				p.gen('(($f.typ (*)())(${iname}_name_table[${var}._interface_idx][$idx]))(${var}._object')
 				receiver_is_interface = true
 			}

vlib/compiler/tests/interface_test.v

@@ -33,6 +33,7 @@ fn perform_speak(s Speaker) {
 	assert true
 	name := s.name()
 	assert name == 'Dog' || name == 'Cat'
+	println(s.name())
 }
 
 fn perform_speakers(speakers []Speaker) {
@@ -70,6 +71,3 @@ fn test_register() {
 	f.register()
 	handle_reg(f)
 }
-
-
-