overlapping memcpy

--- src/xsane.c.orig	Tue Nov 16 21:57:51 2010
+++ src/xsane.c	Thu Dec  4 13:54:42 2014
@@ -4892,7 +4892,7 @@ static void xsane_device_dialog(void)
  char buf[TEXTBUFSIZE];
  char windowname[TEXTBUFSIZE];
  char devicetext[TEXTBUFSIZE];
- char *textptr;
+ char *cp, *textptr;
  GtkWidget *xsane_window;
  GtkWidget *xsane_vbox_main;
  GtkWidget *xsane_vbox_standard;
@@ -4993,8 +4993,8 @@ static void xsane_device_dialog(void)
     textptr = devicetext + strlen(devicetext);
   }
 
-  snprintf(buf, sizeof(buf), ":%s", devname);
-  snprintf(buf, sizeof(buf), "/%s", (strrchr(buf, ':')+1));
+  cp = strrchr(devname, ':');
+  snprintf(buf, sizeof(buf), "/%s", cp ? cp + 1 : devname);
   sprintf(textptr, "%s", (strrchr(buf, '/')+1));
 
   xsane.device_text = strdup(devicetext);