Fix error check in trampoline.c (#569)

The appsec helper library calls a dlopen during during constructors that
may fail. Without clearing it, a call to dlerror() after a successful
call to dlsym() will return the previous error message.

Author: cataphract

spawn_worker/src/trampoline.c

@@ -74,6 +74,9 @@ int main(int argc, char *argv[]) {
       return 10;
     }
 
+    // clear any previous errors
+    (void)dlerror();
+
     void (*fn)() = dlsym(handle, symbol_name);
     char *error = NULL;
 
@@ -122,4 +125,4 @@ int main(int argc, char *argv[]) {
   }
 
   return 12;
-}
+}