x11/leechcraft: unbreak with hunspell 1.5

• Could NOT find HUNSPELL (missing: HUNSPELL_LIBRARIES)

[...]
CMake Error: The following variables are used in this project, but they are set to NOTFOUND.
Please set them or make sure they are set and tested correctly in the CMake files:
HUNSPELL_LIBRARIES (ADVANCED)

linked by target "leechcraft_rosenthal" in directory src/plugins/rosenthal

PR: 214837
Approved by: portmgr blanket