patch 9.0.0188: strange effects when using "text_align" with non-zero column

Problem:    Strange effects when using virtual text with "text_align" and
            non-zero column. (Martin Tournoij)
Solution:   Give an error. (closes #10888)
diff --git a/src/textprop.c b/src/textprop.c
index 45023e8..f33edc2 100644
--- a/src/textprop.c
+++ b/src/textprop.c
@@ -488,6 +488,11 @@
 
 	    if (p == NULL)
 		goto theend;
+	    if (start_col != 0)
+	    {
+		emsg(_(e_can_only_use_text_align_when_column_is_zero));
+		goto theend;
+	    }
 	    if (STRCMP(p, "right") == 0)
 		flags |= TP_FLAG_ALIGN_RIGHT;
 	    else if (STRCMP(p, "below") == 0)