linux-capture: Fail when libdrm missing

I forgot to extend the FATAL_ERROR messages to include libdrm.

plugins/linux-capture/CMakeLists.txt

@@ -47,13 +47,15 @@ set(linux-capture_LIBRARIES
 option(ENABLE_PIPEWIRE "Enable PipeWire support" ON)
 if(ENABLE_PIPEWIRE)
 	find_package(PipeWire QUIET)
-	find_package(Libdrm) # we require libdrm/drm_fourcc.h to build
+	find_package(Libdrm QUIET) # we require libdrm/drm_fourcc.h to build
 	find_package(Gio QUIET)
 
 	if(NOT PIPEWIRE_FOUND)
 		message(FATAL_ERROR "PipeWire library not found! Please install PipeWire or set ENABLE_PIPEWIRE=OFF")
 	elseif(NOT GIO_FOUND)
 		message(FATAL_ERROR "Gio library not found! Please install GLib2 (or Gio) or set ENABLE_PIPEWIRE=OFF")
+	elseif(NOT LIBDRM_INCLUDE_DIRS)
+		message(FATAL_ERROR "libdrm headers not found! Please install libdrm or set ENABLE_PIPEWIRE=OFF")
 	endif()
 
 	add_definitions(-DENABLE_PIPEWIRE)