patch 9.0.0430: cannot use repeat() with a blob

Problem:    Cannot use repeat() with a blob.
Solution:   Implement blob repeat. (closes #11090)
diff --git a/src/testdir/test_blob.vim b/src/testdir/test_blob.vim
index 46370c4..b0239fd 100644
--- a/src/testdir/test_blob.vim
+++ b/src/testdir/test_blob.vim
@@ -725,6 +725,18 @@
   call assert_equal(v, string(b))
 endfunc
 
+func Test_blob_repeat()
+  call assert_equal(0z, repeat(0z00, 0))
+  call assert_equal(0z00, repeat(0z00, 1))
+  call assert_equal(0z0000, repeat(0z00, 2))
+  call assert_equal(0z00000000, repeat(0z0000, 2))
+
+  call assert_equal(0z, repeat(0z12, 0))
+  call assert_equal(0z, repeat(0z1234, 0))
+  call assert_equal(0z1234, repeat(0z1234, 1))
+  call assert_equal(0z12341234, repeat(0z1234, 2))
+endfunc
+
 " Test for blob allocation failure
 func Test_blob_alloc_failure()
   " blob variable