tests: fix QCoreApplication parameters

The argument count (first parameter) is a reference, and thus must be
kept alive for the whole lifetime of the QCoreApplication instance,
as also the Qt apidocs say.

Also properly create a "string array" for the actual args, instead
of badly casting a string to that.

This fixes sporadic crashes in this test.

src/tests/TestImport.cpp

@@ -14,9 +14,9 @@ TestImport::TestImport()
     // Init basic application
     // The app needs to be initialized for the utf8 test
     // to work
-    int argcount = 1;
-    const char* appname = "sqlb-unittests";
-    app = new QCoreApplication(argcount, const_cast<char**>(&appname));
+    argcount = 1;
+    args[0] = "sqlb-unittests";
+    app = new QCoreApplication(argcount, args);
 }
 
 TestImport::~TestImport()

src/tests/TestImport.h

@@ -13,6 +13,8 @@ public:
     ~TestImport();
 
 private:
+    int argcount;
+    char *args[1]; // the size must match what 'argcount' is set to
     QCoreApplication* app;
 
 private slots: