crypto.ecdsa: improves internal function of calc_digest_with_evpkey (#23901)

Author: blackshirt

vlib/crypto/ecdsa/ecdsa.v

@@ -318,12 +318,6 @@ fn calc_digest_with_evpkey(key &C.EVP_PKEY, message []u8, opt SignerOpts) ![]u8
 	if message.len == 0 {
 		return error('null-length messages')
 	}
-	bits_size := C.EVP_PKEY_get_bits(key)
-	if bits_size <= 0 {
-		return error(' bits_size was invalid')
-	}
-	key_size := (bits_size + 7) / 8
-
 	match opt.hash_config {
 		.with_no_hash, .with_recommended_hash {
 			md := default_digest(key)!
@@ -337,6 +331,7 @@ fn calc_digest_with_evpkey(key &C.EVP_PKEY, message []u8, opt SignerOpts) ![]u8
 			if cfg.custom_hash == unsafe { nil } {
 				return error('Custom hasher was not defined')
 			}
+			key_size := evp_key_size(key)!
 			if key_size > cfg.custom_hash.size() {
 				if !cfg.allow_smaller_size {
 					return error('Hash into smaller size than current key size was not allowed')