Avoid diagnostic message forcing crashing the compiler (#19113)

Using issue #18650 as the reference (but issue #18999 is another option)
building on the fix in PR #18719 (refined in PR #18727) as well as the
fix in PR #18760, I'm trying to make a more root change here by making
sure that message forcing only occurs with `hasErrors`/`errorsReported`
is true, so as to avoid assertion errors crashing the compiler.

compiler/src/dotty/tools/dotc/report.scala

@@ -155,6 +155,7 @@ object report:
        |  An unhandled exception was thrown in the compiler.
        |  Please file a crash report here:
        |  https://github.com/lampepfl/dotty/issues/new/choose
+       |  For non-enriched exceptions, compile with -Yno-enrich-error-messages.
        |
        |$info1
        |""".stripMargin

compiler/src/dotty/tools/dotc/reporting/HideNonSensicalMessages.scala

@@ -13,8 +13,8 @@ trait HideNonSensicalMessages extends Reporter {
    */
   override def isHidden(dia: Diagnostic)(using Context): Boolean =
     super.isHidden(dia) || {
-        dia.msg.isNonSensical &&
-        hasErrors && // if there are no errors yet, report even if diagnostic is non-sensical
-        !ctx.settings.YshowSuppressedErrors.value
+        hasErrors  // if there are no errors yet, report even if diagnostic is non-sensical
+        && dia.msg.isNonSensical // defer forcing the message by calling hasErrors first
+        && !ctx.settings.YshowSuppressedErrors.value
     }
 }

compiler/src/dotty/tools/dotc/reporting/Reporter.scala

@@ -155,8 +155,6 @@ abstract class Reporter extends interfaces.ReporterResult {
       addUnreported(key, 1)
     case _                                                  =>
       if !isHidden(dia) then // avoid isHidden test for summarized warnings so that message is not forced
-        markReported(dia)
-        withMode(Mode.Printing)(doReport(dia))
         dia match {
           case w: Warning =>
             warnings = w :: warnings
@@ -169,6 +167,8 @@ abstract class Reporter extends interfaces.ReporterResult {
           case _: Info    => // nothing to do here
           // match error if d is something else
         }
+        markReported(dia)
+        withMode(Mode.Printing)(doReport(dia))
   end issueUnconfigured
 
   def issueIfNotSuppressed(dia: Diagnostic)(using Context): Unit =