Provide more info in case of write failure

src/openrct2/core/FileStream.cpp

@@ -184,9 +184,11 @@ namespace OpenRCT2
         {
             return;
         }
-        if (fwrite(buffer, static_cast<size_t>(length), 1, _file) != 1)
+        if (auto count = fwrite(buffer, static_cast<size_t>(length), 1, _file); count != 1)
         {
-            throw IOException("Unable to write to file.");
+            std::string error = "Unable to write " + std::to_string(length) + " bytes to file. Count = " + std::to_string(count)
+                + ", errno = " + std::to_string(errno);
+            throw IOException(error);
         }
 
         uint64_t position = GetPosition();