patch 8.1.0802: negative index doesn't work for Blob
Problem: Negative index doesn't work for Blob.
Solution: Make it work, add a test. (closes #3856)
diff --git a/src/proto/blob.pro b/src/proto/blob.pro
index b8e48de..019692d 100644
--- a/src/proto/blob.pro
+++ b/src/proto/blob.pro
@@ -6,7 +6,7 @@
void blob_free(blob_T *b);
void blob_unref(blob_T *b);
long blob_len(blob_T *b);
-char_u blob_get(blob_T *b, int idx);
+int blob_get(blob_T *b, int idx);
void blob_set(blob_T *b, int idx, char_u c);
int blob_equal(blob_T *b1, blob_T *b2);
int read_blob(FILE *fd, blob_T *blob);