tree: Don't return empty localname in xmlSplitQName{2,3}

Match the behavior of xmlSplitQName and xmlSplitQName4.
diff --git a/tree.c b/tree.c
index 0e72931..68973e1 100644
--- a/tree.c
+++ b/tree.c
@@ -226,7 +226,7 @@
     while ((name[len] != 0) && (name[len] != ':'))
 	len++;
 
-    if (name[len] == 0)
+    if ((name[len] == 0) || (name[len+1] == 0))
 	return(NULL);
 
     *prefix = xmlStrndup(name, len);
@@ -274,7 +274,7 @@
     while ((name[l] != 0) && (name[l] != ':'))
 	l++;
 
-    if (name[l] == 0)
+    if ((name[l] == 0) || (name[l+1] == 0))
 	return(NULL);
 
     *len = l;