Replace misleading error message when loading PEM

The error message "short header" when the end line
of PEM data cannot be identified is misleading.
Replace it with already existing "bad end line" error.

Fixes #8815
Reviewed-by: NBen Kaduk <kaduk@mit.edu>
(Merged from https://github.com/openssl/openssl/pull/11793)

crypto/pem/pem_lib.c

@@ -824,7 +824,7 @@ static int get_header_and_data(BIO *bp, BIO **header, BIO **data, char *name,
         flags_mask = ~0u;
         len = BIO_gets(bp, linebuf, LINESIZE);
         if (len <= 0) {
-            PEMerr(PEM_F_GET_HEADER_AND_DATA, PEM_R_SHORT_HEADER);
+            PEMerr(PEM_F_GET_HEADER_AND_DATA, PEM_R_BAD_END_LINE);
             goto err;
         }