patch 8.2.2757: Vim9: blob tests for legacy and Vim9 script are separate

Problem:    Vim9: blob tests for legacy and Vim9 script are separate.
Solution:   Add CheckLegacyAndVim9Success().  Make blob index assign work.
diff --git a/src/eval.c b/src/eval.c
index 1291b36..2e2ca23 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -1319,23 +1319,12 @@
 
 	    if (lp->ll_range && rettv->v_type == VAR_BLOB)
 	    {
-		int	il, ir;
-
 		if (lp->ll_empty2)
 		    lp->ll_n2 = blob_len(lp->ll_blob) - 1;
 
-		if (lp->ll_n2 - lp->ll_n1 + 1 != blob_len(rettv->vval.v_blob))
-		{
-		    emsg(_("E972: Blob value does not have the right number of bytes"));
+		if (blob_set_range(lp->ll_blob, lp->ll_n1, lp->ll_n2,
+								rettv) == FAIL)
 		    return;
-		}
-		if (lp->ll_empty2)
-		    lp->ll_n2 = blob_len(lp->ll_blob);
-
-		ir = 0;
-		for (il = lp->ll_n1; il <= lp->ll_n2; il++)
-		    blob_set(lp->ll_blob, il,
-			    blob_get(rettv->vval.v_blob, ir++));
 	    }
 	    else
 	    {