ssize_t is not defined on Windows.

And anyway the argument is storing the output `std::string::size` which is a `size_t`

src/zimdump.cpp

@@ -229,7 +229,7 @@ int ZimDumper::listEntriesByNamespace(const std::string ns, bool details)
     return ret;
 }
 
-void write_to_error_directory(const std::string& base, const std::string relpath, const char *content, ssize_t size)
+void write_to_error_directory(const std::string& base, const std::string relpath, const char *content, size_t size)
 {
     createdir(ERRORSDIR, base);
     std::string url = relpath;
@@ -266,7 +266,7 @@ void write_to_error_directory(const std::string& base, const std::string relpath
 #endif
 }
 
-inline void write_to_file(const std::string &base, const std::string& path, const char* data, ssize_t size) {
+inline void write_to_file(const std::string &base, const std::string& path, const char* data, size_t size) {
     std::string fullpath = base + path;
 #ifdef _WIN32
     std::wstring wpath = utf8ToUtf16(fullpath);