Fix cmake build system bug not generating versioned library name in case LT_REVISION is zero.

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=89450Reviewed-by: Simon McVittie <simon.mcvittie@collabora.co.uk>

cmake/dbus/CMakeLists.txt

@@ -259,12 +259,12 @@ add_library(dbus-1 SHARED
 			${libdbus_SOURCES}
 			${libdbus_HEADERS}
 )
-if(DBUS_LIBRARY_REVISION)
+if(DEFINED DBUS_LIBRARY_REVISION)
     math(EXPR DBUS_LIBRARY_MAJOR "${DBUS_LIBRARY_CURRENT} - ${DBUS_LIBRARY_AGE}")
 endif()
 
 if(WIN32)
-    if(DBUS_LIBRARY_REVISION)
+    if(DEFINED DBUS_LIBRARY_REVISION)
         get_target_property(LEGACY_FILE_NAME dbus-1 LOCATION)
         set_target_properties(dbus-1 PROPERTIES SUFFIX "-${DBUS_LIBRARY_MAJOR}${CMAKE_SHARED_LIBRARY_SUFFIX}")
         add_custom_command(TARGET dbus-1 POST_BUILD
@@ -279,7 +279,7 @@ if(WIN32)
         target_link_libraries(dbus-1 ws2_32 advapi32 netapi32 iphlpapi)
     endif(WINCE)
 else(WIN32)
-    if(DBUS_LIBRARY_REVISION)
+    if(DEFINED DBUS_LIBRARY_REVISION)
         set_target_properties(dbus-1 PROPERTIES VERSION ${DBUS_LIBRARY_MAJOR}.${DBUS_LIBRARY_AGE}.${DBUS_LIBRARY_REVISION} SOVERSION ${DBUS_LIBRARY_MAJOR})
     endif()
     target_link_libraries(dbus-1 ${CMAKE_THREAD_LIBS_INIT} rt)