lib/sqlite: disable if -Ddatabase=false

Fixes build failure in StickerCommands.cxx.

NEWS

@@ -1,6 +1,7 @@
 ver 0.21.17 (not yet released)
 * outputs
   - jack: mark ports as terminal
+* fix build failure with -Ddatabase=false
 
 ver 0.21.16 (2019/10/16)
 * queue

src/lib/sqlite/meson.build

@@ -1,4 +1,9 @@
-sqlite_dep = dependency('sqlite3', version: '>= 3.7.3', required: get_option('sqlite'))
+if enable_database
+  sqlite_dep = dependency('sqlite3', version: '>= 3.7.3', required: get_option('sqlite'))
+else
+  sqlite_dep = dependency('', required: false)
+endif
+
 conf.set('ENABLE_SQLITE', sqlite_dep.found())
 if not sqlite_dep.found()
   subdir_done()