Fixed issue #25: invalid file cnt and sel in thumb mode

Makefile

@@ -1,4 +1,4 @@
-VERSION = git-20111027
+VERSION = git-20111031
 
 CC      = gcc
 CFLAGS  = -ansi -Wall -pedantic -O2

commands.c

@@ -69,7 +69,10 @@ bool it_switch_mode(arg_t a) {
 			img.slideshow = false;
 			reset_timeout(slideshow);
 		}
-		tns.sel = fileidx;
+		if (fileidx < tns.cnt)
+			tns.sel = fileidx;
+		else
+			tns.sel = tns.cnt > 0 ? tns.cnt - 1 : 0;
 		tns.dirty = true;
 		mode = MODE_THUMB;
 	} else {