Handle dlsym() failures in chainloaders better

If these ever fail (because the function names change, not that that
should happen anytime soon) then you'll now get the expected logging
output instead of it just printing an assertion failure to the terminal.

src/chainloader/vst2-chainloader.cpp

@@ -76,7 +76,10 @@ bool initialize_library() {
     do {                                                                    \
         (name) =                                                            \
             reinterpret_cast<decltype(name)>(dlsym(library_handle, #name)); \
-        assert(name);                                                       \
+        if (!(name)) {                                                      \
+            log_failing_dlsym(yabridge_vst2_plugin_name, #name);            \
+            return false;                                                   \
+        }                                                                   \
     } while (false)
 
     LOAD_FUNCTION(yabridge_plugin_init);