Fix #7217: add test

Author: liufengyun

tests/pos/i7217.scala

@@ -0,0 +1,5 @@
+class Foo(p1: String, p2: String):
+  def this(p1: String) = this(p1, "blah")
+
+val x = { Foo("blah", "hah") }
+val y = { Foo("blah") }