patch 8.2.3787: no proper formatting of a C line comment after a statement

Problem:    No proper formatting of a C line comment after a statement.
Solution:   Find the start of the line comment, insert the comment leader and
            indent the comment properly.
diff --git a/src/testdir/test_cindent.vim b/src/testdir/test_cindent.vim
index c097ca7..c7ce2ba 100644
--- a/src/testdir/test_cindent.vim
+++ b/src/testdir/test_cindent.vim
@@ -1694,9 +1694,9 @@
   #endif
 
   int y;		// comment
-  // comment
+			// comment
 
-  // comment
+			// comment
 
   {
   	Constructor(int a,