Future-proof source for changes in xdemitconf_t

The instances of xdemitconf_t were initialized member by member.
Instead, initialize them to all zero, so we do not have
to update those places each time we introduce a new member.

[jc: minimally fixed by getting rid of a new global]

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/diff.c b/diff.c
index 16ea710..d10e848 100644
--- a/diff.c
+++ b/diff.c
@@ -390,6 +390,7 @@
 	mmfile_t minus, plus;
 	int i;
 
+	memset(&xecfg, 0, sizeof(xecfg));
 	minus.size = diff_words->minus.text.size;
 	minus.ptr = xmalloc(minus.size);
 	memcpy(minus.ptr, diff_words->minus.text.ptr, minus.size);
@@ -408,7 +409,6 @@
 
 	xpp.flags = XDF_NEED_MINIMAL;
 	xecfg.ctxlen = diff_words->minus.alloc + diff_words->plus.alloc;
-	xecfg.flags = 0;
 	ecb.outf = xdiff_outf;
 	ecb.priv = diff_words;
 	diff_words->xm.consume = fn_out_diff_words_aux;
@@ -1218,6 +1218,7 @@
 		xdemitcb_t ecb;
 		struct emit_callback ecbdata;
 
+		memset(&xecfg, 0, sizeof(xecfg));
 		memset(&ecbdata, 0, sizeof(ecbdata));
 		ecbdata.label_path = lbl;
 		ecbdata.color_diff = o->color_diff;
@@ -1286,9 +1287,8 @@
 		xdemitconf_t xecfg;
 		xdemitcb_t ecb;
 
+		memset(&xecfg, 0, sizeof(xecfg));
 		xpp.flags = XDF_NEED_MINIMAL | o->xdl_opts;
-		xecfg.ctxlen = 0;
-		xecfg.flags = 0;
 		ecb.outf = xdiff_outf;
 		ecb.priv = diffstat;
 		xdl_diff(&mf1, &mf2, &xpp, &xecfg, &ecb);
@@ -1326,9 +1326,8 @@
 		xdemitconf_t xecfg;
 		xdemitcb_t ecb;
 
+		memset(&xecfg, 0, sizeof(xecfg));
 		xpp.flags = XDF_NEED_MINIMAL;
-		xecfg.ctxlen = 0;
-		xecfg.flags = 0;
 		ecb.outf = xdiff_outf;
 		ecb.priv = &data;
 		xdl_diff(&mf1, &mf2, &xpp, &xecfg, &ecb);
@@ -2780,6 +2779,7 @@
 		struct diff_filepair *p = q->queue[i];
 		int len1, len2;
 
+		memset(&xecfg, 0, sizeof(xecfg));
 		if (p->status == 0)
 			return error("internal diff status error");
 		if (p->status == DIFF_STATUS_UNKNOWN)