Don't insert INDENT/UNINDENT without anything in between

Fixes #14061

Author: odersky

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

@@ -539,7 +539,7 @@ object Scanners {
            || nextWidth == lastWidth && (indentPrefix == MATCH || indentPrefix == CATCH) && token != CASE then
           if currentRegion.isOutermost then
             if nextWidth < lastWidth then currentRegion = topLevelRegion(nextWidth)
-          else if !isLeadingInfixOperator(nextWidth) && !statCtdTokens.contains(lastToken) then
+          else if !isLeadingInfixOperator(nextWidth) && !statCtdTokens.contains(lastToken) && lastToken != INDENT then
             currentRegion match
               case r: Indented =>
                 currentRegion = r.enclosing