cmake: reenable the search of the JPEG library

there is no more a top-level CMakeLists.txt searching it;
this makes the plucker backend compilable again
(cherry picked from commit 41c57246)

generators/CMakeLists.txt

@@ -20,9 +20,8 @@ macro_log_feature(TIFF_FOUND "libTIFF" "A library for reading and writing TIFF f
 macro_optional_find_package(Freetype)
 macro_log_feature(FREETYPE_FOUND "FreeType" "A font rendering engine" "http://www.freetype.org" FALSE "" "Provides freetype font support in the okular DVI generator.")
 
-#we look for JPEG in kdegraphics/CMakeLists.txt
-#macro_optional_find_package(JPEG)
-#macro_log_feature(JPEG_FOUND "JPEG" "A library for reading and writing JPEG image files." "http://www.ijg.org" FALSE "" "Support fof PalmDB documents in okular.")
+macro_optional_find_package(JPEG)
+macro_log_feature(JPEG_FOUND "JPEG" "A library for reading and writing JPEG image files." "http://www.ijg.org" FALSE "" "Support fof PalmDB documents in okular.")
 macro_optional_find_package(ZLIB)
 macro_log_feature(ZLIB_FOUND "ZLib" "The Zlib compression library" "http://www.zlib.net" FALSE "" "Support for Plucker files in Okular.")