Fix use of uninitialized variables

Building with optimization in debug mode revealed code that could in
theory result in undefined behavior.

server/modules/filter/cache/test/testkeygeneration.cc

@@ -123,7 +123,7 @@ int test(StorageFactory& factory, istream& in)
 int main(int argc, char* argv[])
 {
     int rv = EXIT_FAILURE;
-    StorageFactory* pFactory;
+    StorageFactory* pFactory = nullptr;
     if ((argc == 2) || (argc == 3))
     {
         char* libdir = MXS_STRDUP("../../../../../query_classifier/qc_sqlite/");

server/modules/filter/hintfilter/hintparser.cc

@@ -131,7 +131,9 @@ HINT* hint_parser(HINT_SESSION* session, GWBUF* request)
     int len, residual, state;
     int found, escape, quoted, squoted;
     HINT* rval = NULL;
-    char* pname, * lvalue, * hintname = NULL;
+    char* pname = nullptr;
+    char* lvalue = nullptr;
+    char* hintname = nullptr;
     GWBUF* buf;
     HINT_TOKEN* tok;
     HINT_MODE mode = HM_EXECUTE;

server/modules/filter/tpmfilter/tpmfilter.cc

@@ -740,7 +740,7 @@ static void destroyInstance(MXS_FILTER* instance)
 
 static void checkNamedPipe(TPM_INSTANCE* inst)
 {
-    int ret;
+    int ret = 0;
     char buffer[2];
     char buf[4096];
     char* named_pipe = inst->named_pipe;