refine condition for checking override

Author: liufengyun

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

@@ -810,12 +810,14 @@ class RefChecks extends MiniPhase { thisTransformer =>
           cls.owner.info.baseClasses.exists(_.info.member(cls.name).exists)
       }
 
+      val errors = ctx.reporter.errorCount
+
       // If owner is possibly problematic, check owner first.
       // If there are overriding errors with owner, stop checking current to avoid cyclic reference.
       // See neg/i1750.scala.
       if (ownerPossibleProblematic(cls)) checkAllOverrides(cls.owner)
 
-      if (!ctx.reporter.hasErrors) checkAllOverrides(cls)
+      if (ctx.reporter.errorCount == errors) checkAllOverrides(cls)
       tree
     } catch {
       case ex: MergeError =>