fix: Providers not being closed correctly

Fixes #692

lib/libimhex/source/api/imhex_api.cpp

@@ -307,6 +307,7 @@ namespace hex {
             else if (it - s_providers.begin() == s_currentProvider)
                 setCurrentProvider(0);
 
+            provider->close();
             delete provider;
         }
 

lib/libimhex/source/providers/provider.cpp

@@ -19,7 +19,6 @@ namespace hex::prv {
     Provider::~Provider() {
         for (auto &overlay : this->m_overlays)
             this->deleteOverlay(overlay);
-        this->close();
     }
 
     void Provider::read(u64 offset, void *buffer, size_t size, bool overlays) {