patch 8.2.4935: with 'foldmethod' "indent" some lines not included in fold

Problem:    With 'foldmethod' "indent" some lines are not included in the
            fold. (Oleg Koshovetc)
Solution:   Fix it. (Brandon Simmons, closes #10399, closes #3214)
diff --git a/src/fold.c b/src/fold.c
index f94b389..7c51557 100644
--- a/src/fold.c
+++ b/src/fold.c
@@ -2246,7 +2246,14 @@
 	    getlevel = foldlevelDiff;
 #endif
 	else
+	{
 	    getlevel = foldlevelIndent;
+	    // Start one line back, because if the line above "top" has an
+	    // undefined fold level, folding it relies on the line under it,
+	    // which is "top".
+	    if (top > 1)
+		--fline.lnum;
+	}
 
 	// Backup to a line for which the fold level is defined.  Since it's
 	// always defined for line one, we will stop there.