Honor lastErrorOffset in incompleteInoutError

As for the other errors, don't issue an incomplete input error if the
last error offset is the current offset.

compiler/src/dotty/tools/dotc/parsing/Parsers.scala

@@ -267,19 +267,22 @@ object Parsers {
 
     /** Issue an error at current offset that input is incomplete */
     def incompleteInputError(msg: Message): Unit =
-      report.incompleteInputError(msg, source.atSpan(Span(in.offset)))
+      if in.offset != lastErrorOffset then
+        report.incompleteInputError(msg, source.atSpan(Span(in.offset)))
 
     /** If at end of file, issue an incompleteInputError.
      *  Otherwise issue a syntax error and skip to next safe point.
      */
     def syntaxErrorOrIncomplete(msg: Message, offset: Int = in.offset): Unit =
-      if (in.token == EOF) incompleteInputError(msg)
+      if in.token == EOF then
+        incompleteInputError(msg)
       else
         syntaxError(msg, offset)
         skip()
 
     def syntaxErrorOrIncomplete(msg: Message, span: Span): Unit =
-      if (in.token == EOF) incompleteInputError(msg)
+      if in.token == EOF then
+        incompleteInputError(msg)
       else
         syntaxError(msg, span)
         skip()

tests/neg/i2494.scala

@@ -1,3 +1,2 @@
 enum
 object // error
-// error

tests/neg/i4373c.scala

@@ -1,4 +1,3 @@
 // ==> 18b253a4a89a84c5674165c6fc3efafad535eee3.scala <==
 object x0 {
   def x1[x2 <:_[ // error
-// error

tests/neg/i4934.scala

@@ -8,4 +8,4 @@ object Main {
 
 object Foo {
   val a = ""); // error: `}` expected but `)` found
-}
+} // error: eof expected but `}` found

tests/neg/i8731a.scala

@@ -7,4 +7,4 @@ object test:
   for
     a <- Seq()
   end for    // error: `yield` or `do` expected
-  do ()            // error: expression expected but eof found
+  do ()

tests/neg/parser-stability-1.scala

@@ -1,4 +1,3 @@
 object x0 {
 x1 match  // error
 def this // error
-// error

tests/neg/parser-stability-18.scala

@@ -2,4 +2,3 @@ trait x0 {
     class x1 (x1:x0
     {
 type x1 <: List[x1 <:  // error
-// error

tests/neg/parser-stability-19.scala

@@ -2,4 +2,3 @@ object x0 {
   case class x0[]():                  // error
     def x0( ) ]                       // error
     def x0 ( x0:x0 ):x0.type = x1 x0
-// error

tests/neg/parser-stability-2.scala

@@ -1,3 +1,2 @@
 trait x0 {
 new _  // error
-// error