Always try to find dependencies for plugins

Generated plugin CMake files should always try to call
find_dependency, especially in static builds.

pkg_check_modules sets a cache value for foo_FOUND instead of
a directory scope foo_FOUND, which means that find_dependency
will not be called in another scope, and thus fail to create
needed imported targets.

Note this makes the code be the same as in
ModuleDependencies.cmake.in.

Change-Id: I0b58b038afcb72cb27d0b433371bc9cb5e4bfec9
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

cmake/QtPluginDependencies.cmake.in

@@ -10,14 +10,12 @@ foreach(_target_dep ${_third_party_deps})
         list(APPEND find_package_args "${version}")
     endif()
 
-    if (NOT ${pkg}_FOUND)
         if(components)
             string(REPLACE " " ";" components "${components}")
             find_dependency(${find_package_args} COMPONENTS ${components})
         else()
             find_dependency(${find_package_args})
         endif()
-    endif()
 
     if (NOT ${pkg}_FOUND)
         set(@target@_FOUND FALSE)