rego: Parse store modules iff modules set on the Rego object

Currently we parse store modules irrespective of whether
there are modules on the Rego object. This will result in
the compilation of those modules which triggers the bundle
activation flow. Now as part of the module compilation
we interact with the compiler's modules and run compilation
on the input modules. If let's say there are concurrent health
check requests (ie. /v1/health), this could result in a race
during the compilation process while working with the compiler's
modules.

This change avoids this situation by skipping parsing of the store
modules when none are set on the Rego object. The assumption this
change makes is that while using the rego package the compiler and
store are kept in-sync.

Fixes: #5868

Signed-off-by: Ashutosh Narkar <anarkar4387@gmail.com>