verify that the connection is open before trying to close it

src/knowledge_base.cpp

@@ -40,9 +40,12 @@ obelisk::KnowledgeBase::KnowledgeBase(const char* filename, int flags)
 }
 
 obelisk::KnowledgeBase::~KnowledgeBase()
+{
+    if (dbConnection_)
     {
         sqlite3_close_v2(dbConnection_);
     }
+}
 
 void obelisk::KnowledgeBase::createTable(std::function<const char*()> function)
 {

src/knowledge_base.h

@@ -15,7 +15,7 @@ namespace obelisk
             const int DEFAULT_FLAGS
                 = SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE;
             const char* filename_;
-            sqlite3* dbConnection_;
+            sqlite3* dbConnection_ = nullptr;
             int flags_;
             void logSqliteError(int result);