patch 8.2.3510: changes are only detected with one second accuracy

Problem:    Changes are only detected with one second accuracy.
Solution:   Use the nanosecond time if possible.  (Leah Neukirchen,
            closes #8873, closes #8875)
diff --git a/src/netbeans.c b/src/netbeans.c
index bf47df7..5bd36a4 100644
--- a/src/netbeans.c
+++ b/src/netbeans.c
@@ -1760,7 +1760,10 @@
 	    if (buf == NULL || buf->bufp == NULL)
 		nbdebug(("    invalid buffer identifier in setModtime\n"));
 	    else
+	    {
 		buf->bufp->b_mtime = atoi((char *)args);
+		buf->bufp->b_mtime_ns = 0;
+	    }
 // =====================================================================
 	}
 	else if (streq((char *)cmd, "setReadOnly"))