Add type casts for mg_base64_decode

fixes civetweb#1073 but does not change the interface

src/civetweb.c

@@ -8519,7 +8519,7 @@ parse_auth_header(struct mg_connection *conn,
 		const char *userpw_b64 = auth_header + 6;
 		size_t userpw_b64_len = strlen(userpw_b64);
 		size_t buf_len_r = buf_size;
-		if (mg_base64_decode(userpw_b64, userpw_b64_len, buf, &buf_len_r)
+		if (mg_base64_decode(userpw_b64, userpw_b64_len, (unsigned char *)buf, &buf_len_r)
 		    != -1) {
 			return 0; /* decode error */
 		}

unittest/public_func.c

@@ -589,23 +589,23 @@ START_TEST(test_mg_base64)
 
 	memset(buf, 77, sizeof(buf));
 	len = 9999;
-	mg_base64_encode((unsigned char *)alpha, (int)strlen(alpha), buf, &len);
+	mg_base64_encode((unsigned char *)alpha, strlen(alpha), buf, &len);
 	ck_assert_str_eq(buf, alpha_b64_enc);
 	ck_assert_int_eq((int)len, (int)strlen(alpha_b64_enc) + 1);
 
 	memset(buf, 77, sizeof(buf));
 	len = 9999;
 	mg_base64_encode((unsigned char *)nonalpha,
-	                 (int)strlen(nonalpha),
-	                 (unsigned char *)buf,
+	                 strlen(nonalpha),
+	                 (char *)buf,
 	                 &len);
 	ck_assert_str_eq(buf, nonalpha_b64_enc);
 	ck_assert_int_eq((int)len, (int)strlen(nonalpha_b64_enc) + 1);
 
 	memset(buf, 77, sizeof(buf));
 	len = 9999;
 	ret = mg_base64_decode((char *)alpha_b64_enc,
-	                       (int)strlen(alpha_b64_enc),
+	                       strlen(alpha_b64_enc),
 	                       (unsigned char *)buf,
 	                       &len);
 	ck_assert_int_eq(ret, -1);