Bug 1849518 - Add null after call to FileLocation::GetBaseFile r=jesup a=pascalc

Differential Revision: https://phabricator.services.mozilla.com/D187537

mozglue/misc/MmapFaultHandler.h

@@ -89,7 +89,9 @@ inline bool ValidFD(T fd) {
       }                                                        \
       if (ValidFD(fd) && fd->mFile) {                          \
         nsCOMPtr<nsIFile> file = fd->mFile.GetBaseFile();      \
-        file->GetNativeLeafName(mmapScopeFilename);            \
+        if (file) {                                            \
+          file->GetNativeLeafName(mmapScopeFilename);          \
+        }                                                      \
       }                                                        \
       MmapAccessScope mmapScope(mmapScopeBuf, mmapScopeBufLen, \
                                 mmapScopeFilename.get());      \