Another leak fixed

It's really hard to weaken assertions so that they can deal with all
possible random crap input.

Author: odersky

compiler/src/dotty/tools/dotc/typer/Checking.scala

@@ -718,7 +718,7 @@ trait Checking {
       val conv =
         if (sym.isOneOf(GivenOrImplicit) || sym.info.isErroneous) sym
         else {
-          assert(sym.name == nme.apply)
+          assert(sym.name == nme.apply || ctx.reporter.errorsReported)
           sym.owner
         }
       val conversionOK =

tests/neg/i7750a.scala

@@ -0,0 +1,5 @@
+def foo: Unit = {
+    val a = (x: Int, y: String) => x + + y  // error
+    implicit def f[X](x: (X,  String) => String) = (z: X) => (z, null) // error
+    a(1)
+}