Merge pull request #12191 from dotty-staging/fix-#12180

Add regression test

Author: nicolasstucki

tests/pos/i12180a.scala

@@ -0,0 +1,7 @@
+inline def n = null
+inline def f = inline if n == null then 0 else 1
+inline def m = inline n match { case null => 0; case _ => 1 }
+
+@main def main =
+  println(f) // error
+  println(m)

tests/pos/i12180b.scala

@@ -0,0 +1,9 @@
+inline def n = "im a string"
+inline def f = inline if n == null then 0 else 1
+inline def g = inline if null == n then 0 else 1
+inline def m = inline n match { case null => 0; case _ => 1 }
+
+@main def main =
+  println(f)
+  println(g)
+  println(m)