HEIF loader: Call heif_[de]init() on loader load/unload

Seems to be required as of libheif-1.16.

Note - Running the tests with valgrind shows no problems, but with asan
enabled I get a bunch of messages like:

Direct leak of 8 byte(s) in 1 object(s) allocated from:
    #0 0x7f186d98ee38 in operator new(unsigned long) (/lib64/libasan.so.8+0xd9e38) (BuildId: bac59ca9f1e357781008d7f6982314d30ca62672)
    #1 0x7f186c4acec9 in ColorConversionPipeline::init_ops() [clone .part.0] (/lib64/libheif.so.1+0x6fec9) (BuildId: 2823b8c3a24fbf4262672d27ed3bf5a338d185b5)
    #2 0x7f186c4a2dec in heif_init (/lib64/libheif.so.1+0x65dec) (BuildId: 2823b8c3a24fbf4262672d27ed3bf5a338d185b5)
    #3 0x7f186d824d4e in __imlib_ProduceLoader ../../../../src/lib/loaders.c:209

src/modules/loaders/loader_heif.c

@@ -172,4 +172,21 @@ _load(ImlibImage * im, int load_data)
    return rc;
 }
 
+#if !LIBHEIF_HAVE_VERSION(1, 13, 0)
+
 IMLIB_LOADER_KEEP(_formats, _load, NULL);
+
+#else
+
+static void
+_inex(int init)
+{
+   if (init)
+      heif_init(NULL);
+   else
+      heif_deinit();
+}
+
+IMLIB_LOADER_INEX(_formats, _load, NULL, _inex);
+
+#endif