Prevent infinite recursion with nested table and textarea

Bug-Debian: https://github.com/tats/w3m/issues/20#issuecomment-260590257

file.c

@@ -6448,6 +6448,7 @@ HTMLlineproc0(char *line, struct html_feed_environ *h_env, int internal)
 		    do_blankline(h_env, obuf, indent, 0, h_env->limit);
 		}
 		save_fonteffect(h_env, obuf);
+		initRenderTable();
 		renderTable(tbl, tbl_width, h_env);
 		restore_fonteffect(h_env, obuf);
 		obuf->flag &= ~RB_IGNORE_P;

proto.h

@@ -393,6 +393,7 @@ extern void align(TextLine *lbuf, int width, int mode);
 extern void print_item(struct table *t, int row, int col, int width, Str buf);
 extern void print_sep(struct table *t, int row, int type, int maxcol, Str buf);
 extern void do_refill(struct table *tbl, int row, int col, int maxlimit);
+extern void initRenderTable(void);
 extern void renderTable(struct table *t, int max_width,
 			struct html_feed_environ *h_env);
 extern struct table *begin_table(int border, int spacing, int padding,

table.c

@@ -1623,6 +1623,15 @@ get_table_width(struct table *t, short *orgwidth, short *cellwidth, int flag)
 #define fixed_table_width(t)\
   (get_table_width(t,t->fixed_width,t->cell.fixed_width,CHECK_MINIMUM))
 
+#define MAX_COTABLE_LEVEL 100
+static int cotable_level;
+
+void
+initRenderTable(void)
+{
+    cotable_level = 0;
+}
+
 void
 renderCoTable(struct table *tbl, int maxlimit)
 {
@@ -1633,6 +1642,10 @@ renderCoTable(struct table *tbl, int maxlimit)
     int i, col, row;
     int indent, maxwidth;
 
+    if (cotable_level >= MAX_COTABLE_LEVEL)
+	return;	/* workaround to prevent infinite recursion */
+    cotable_level++;
+
     for (i = 0; i < tbl->ntable; i++) {
 	t = tbl->tables[i].ptr;
 	col = tbl->tables[i].col;