Add comment highlighting known fragile code

We know we can't make the struct bigger as everything caught fire when we gave freeze dumps their own path, and was fixed when we switched to a common directory and just separate filenames.
Switching to wchar_t and stopping using UTF-8 here would cause a similar size increase, so similar problems are to be expected.

components/crashcatcher/windowscrashshm.hpp

@@ -40,6 +40,8 @@ namespace Crash
             HANDLE mSignalApp;
             HANDLE mSignalMonitor;
             HANDLE mShmMutex;
+            // the size defines are in UTF-16 code units, and lots of things use more UTF-8 code units, so this may explode with really long non-ASCII paths
+            // we can't switch to wchar_t as when we've made this struct bigger in the past, things exploded
             char mDumpDirectoryPath[MAX_LONG_PATH];
             char mCrashDumpFileName[MAX_FILENAME];
             char mFreezeDumpFileName[MAX_FILENAME];