Add back the missing MAGNUM_PLUGINS_INSTALL_DIR variable.

Caused the utilities to have empty plugin dir by default. Broken since
the debug/release library separation.

CMakeLists.txt

@@ -194,6 +194,15 @@ set(MAGNUM_PLUGINS_INCLUDE_INSTALL_DIR ${CMAKE_INSTALL_PREFIX}/include/MagnumPlu
 # Separate install dirs for debug and release plugins
 set(MAGNUM_PLUGINS_DEBUG_INSTALL_DIR ${MAGNUM_LIBRARY_INSTALL_DIR}/magnum-d)
 set(MAGNUM_PLUGINS_RELEASE_INSTALL_DIR ${MAGNUM_LIBRARY_INSTALL_DIR}/magnum)
+
+# Plugin installation dirs based on wheter we are in debug or release build,
+# needed by some command-line tools
+if(CMAKE_BUILD_TYPE STREQUAL "Debug")
+    set(MAGNUM_PLUGINS_INSTALL_DIR ${MAGNUM_PLUGINS_DEBUG_INSTALL_DIR})
+else()
+    set(MAGNUM_PLUGINS_INSTALL_DIR ${MAGNUM_PLUGINS_RELEASE_INSTALL_DIR})
+endif()
+
 set(MAGNUM_PLUGINS_FONT_DEBUG_INSTALL_DIR ${MAGNUM_PLUGINS_DEBUG_INSTALL_DIR}/fonts)
 set(MAGNUM_PLUGINS_FONT_RELEASE_INSTALL_DIR ${MAGNUM_PLUGINS_RELEASE_INSTALL_DIR}/fonts)
 set(MAGNUM_PLUGINS_FONTCONVERTER_DEBUG_INSTALL_DIR ${MAGNUM_PLUGINS_DEBUG_INSTALL_DIR}/fontconverters)