patch 8.1.0105: all tab stops are the same

Problem:    All tab stops are the same.
Solution:   Add the variable tabstop feature. (Christian Brabandt,
            closes #2711)
diff --git a/src/beval.c b/src/beval.c
index 4ceddca..74750a2 100644
--- a/src/beval.c
+++ b/src/beval.c
@@ -124,6 +124,11 @@
 		*lnump = lnum;
 		*textp = lbuf;
 		*colp = col;
+#ifdef FEAT_VARTABS
+		if (beval->vts)
+		    vim_free(beval->vts);
+		beval->vts = tabstop_copy(wp->w_buffer->b_p_vts_array);
+#endif
 		beval->ts = wp->w_buffer->b_p_ts;
 		return OK;
 	    }