Fix enabling commands when they need to write a document in certain cases (fix #4310)

In certain situations a script creating a transaction could run
certain commands (or functions running commands) that will ask if the
command is enabled before executing it (Command::executeCommand()).

ContextFlags::update() is the function that checks if we can upgrade a
reader lock to a writer, which means that we can write the
document. The new fix in laf's RWLock::canWriteLockFromRead() makes
this condition work correctly.

laf

@@ -1 +1 @@
-Subproject commit b571c453fc6fcae1744e895a2d279d6f20a5942e
+Subproject commit 763ce0424b96a4dda274b59954314e4af6d64dca