datasets: remove useless NULL check

Coverity did detect that the cleaning code is only reached with
Dataset *set being initialized so the check is useless.

** CID 1649392:       Null pointer dereferences  (REVERSE_INULL)
/src/datasets-context-json.c: 719           in DatajsonGet()
>>>     Null-checking "set" suggests that it may be null, but it has
already been dereferenced on all paths leading to the check.

** CID 1649391:       Null pointer dereferences  (REVERSE_INULL)
/src/datasets.c: 526           in DatasetGet()
>>>     Null-checking "set" suggests that it may be null, but it has
already been dereferenced on all paths leading to the check.

src/datasets-context-json.c

@@ -716,12 +716,10 @@ Dataset *DatajsonGet(const char *name, enum DatasetTypes type, const char *load,
     DatasetUnlock();
     return set;
 out_err:
-    if (set) {
-        if (set->hash) {
-            THashShutdown(set->hash);
-        }
-        SCFree(set);
+    if (set->hash) {
+        THashShutdown(set->hash);
     }
+    SCFree(set);
     DatasetUnlock();
     return NULL;
 }

src/datasets.c

@@ -520,12 +520,10 @@ Dataset *DatasetGet(const char *name, enum DatasetTypes type, const char *save,
     DatasetUnlock();
     return set;
 out_err:
-    if (set) {
-        if (set->hash) {
-            THashShutdown(set->hash);
-        }
-        SCFree(set);
+    if (set->hash) {
+        THashShutdown(set->hash);
     }
+    SCFree(set);
     DatasetUnlock();
     return NULL;
 }