CppEditor: Fix comment conversion for indented comments

Due to accidentally overlapping removal/replace operations, it could
happen that we lost actual content when trying to remove whitespace.
Amends f93836b25d.

Change-Id: I7a624e78cf0986ee9818d47ea0812c6632426a24
Reviewed-by: David Schulz <david.schulz@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>

src/plugins/cppeditor/cppquickfix_test.cpp

@@ -9115,6 +9115,23 @@ int var2;)";
 // A third affected comment
 /* An unaffected comment */)";
 
+    // FIXME: Remove adjacent newline along with last block
+    // FIXME: Use CppRefactoringFile to auto-indent continuation lines?
+    QTest::newRow("C -> C++, indented") << R"(
+struct S {
+    /*
+     * @This is an
+     * indented comment.
+     */
+    void func();
+)" << R"(
+struct S {
+    // This is an
+// indented comment.
+
+    void func();
+)";
+
     QTest::newRow("C++ -> C / no selection / single line") << R"(
 // Other comment, unaffected
 // Our @comment

src/plugins/cppeditor/cppquickfixes.cpp

@@ -9438,6 +9438,7 @@ private:
                     changeSet.remove(block.position() + firstColumn, block.position() + endColumn);
                 };
                 const int contentIndex = indexOfActualContent();
+                int removed = 0;
                 if (contentIndex == -1) {
                     if (blockIsRemovable) {
                         removeBlock();
@@ -9455,6 +9456,7 @@ private:
                 } else {
                     changeSet.remove(block.position() + firstColumn,
                                      block.position() + firstColumn + contentIndex);
+                    removed = contentIndex;
                 }
 
                 if (block == firstBlock) {
@@ -9464,7 +9466,7 @@ private:
                     // If the line starts with enough whitespace, replace it with the
                     // comment start characters, so we don't move the content to the right
                     // unnecessarily. Otherwise, insert the comment start characters.
-                    if (blockText.startsWith(QString(newCommentStart.size() + 1, ' '))) {
+                    if (blockText.startsWith(QString(newCommentStart.size() + removed + 1, ' '))) {
                         changeSet.replace(block.position(),
                                           block.position() + newCommentStart.length(),
                                           newCommentStart);