Aside from the remedy provided by @user535733, you can always check before installing what the apt will do by simulating the install using the -s flag:

apt install -s <package-which-is-already-there>

If the package is already installed you will get a line like this:

<package-which-is-already-there> is already the newest version (<version>).

From the man page man apt-get:

-s, --simulate, --just-print, --dry-run, --recon, --no-act

   No action; perform a simulation of events that would occur based on the

   current system state but do not actually change the system. Locking will be

   disabled (Debug::NoLocking) so the system state could change while apt-get

   is running. Simulations can also be executed by non-root users which might

   not have read access to all apt configuration distorting the simulation. A

   notice expressing this warning is also shown by default for non-root users

   (APT::Get::Show-User-Simulation-Note). Configuration Item:

   APT::Get::Simulate.



   Simulated runs print out a series of lines, each representing a dpkg

   operation: configure (Conf), remove (Remv) or unpack (Inst). Square brackets

   indicate broken packages, and empty square brackets indicate breaks that are

   of no consequence (rare).