patch 9.0.0765: with a Visual block a put command column may go negative

Problem:    With a Visual block a put command column may go negative.
Solution:   Check that the column does not become negative.
diff --git a/src/testdir/test_visual.vim b/src/testdir/test_visual.vim
index 66a44c5..a7f8ec4 100644
--- a/src/testdir/test_visual.vim
+++ b/src/testdir/test_visual.vim
@@ -483,6 +483,18 @@
   bw!
 endfunc
 
+func Test_visual_block_put_invalid()
+  enew!
+  behave mswin
+  norm yy
+  norm v)Ps/^/	
+  " this was causing the column to become negative
+  silent norm ggv)P
+
+  bwipe!
+  behave xterm
+endfunc
+
 " Visual modes (v V CTRL-V) followed by an operator; count; repeating
 func Test_visual_mode_op()
   new