base64.h: Fix return type mismatch

Fixes #25220.

thirdparty/misc/base64.h

@@ -11,8 +11,8 @@
 
 extern "C" {
 
-uint32_t base64_encode(char *to, char *from, uint32_t len);
-uint32_t base64_decode(char *to, char *from, uint32_t len);
+long base64_encode(char *to, char *from, unsigned int len);
+long base64_decode(char *to, char *from, unsigned int len);
 };
 
 #endif /* BASE64_H */