Revert over-eager bailout when trailing whitespace (#28848)

src/services/formatting/formatting.ts

@@ -1106,10 +1106,7 @@ namespace ts.formatting {
          * Trimming will be done for lines after the previous range
          */
         function trimTrailingWhitespacesForRemainingRange() {
-            if (!previousRange) {
-                return;
-            }
-            const startPosition = previousRange.end;
+            const startPosition = previousRange ? previousRange.end : originalRange.pos;
 
             const startLine = sourceFile.getLineAndCharacterOfPosition(startPosition).line;
             const endLine = sourceFile.getLineAndCharacterOfPosition(originalRange.end).line;

tests/cases/fourslash/formatAfterWhitespace.ts

@@ -0,0 +1,14 @@
+/// <reference path="fourslash.ts" />
+////function foo()
+////{
+////    var bar;
+////    /*1*/
+////}
+goTo.marker('1')
+edit.insertLine("");
+verify.currentFileContentIs(`function foo()
+{
+    var bar;
+
+
+}`);