Some fixes found by coverity for things used before a null check

In the second case, we actually check the wrong variable.

obrender/image.c

@@ -243,15 +243,14 @@ RrImageSet* RrImageSetMergeSets(RrImageSet *b, RrImageSet *a)
     gint n_original, n_resized, tmp;
     GSList *it;
 
-    const gint max_resized = a->cache->max_resized_saved;
+    gint max_resized;
 
     if (!a)
         return b;
     if (!b)
         return a;
     if (a == b)
         return b;
-
     /* the original and resized picture lists in an RrImageSet are kept ordered
        as newest to oldest.  we don't have timestamps for them, so we cannot
        preserve this in the merged RrImageSet exactly.  a decent approximation,
@@ -264,6 +263,8 @@ RrImageSet* RrImageSetMergeSets(RrImageSet *b, RrImageSet *a)
 
     g_assert(b->cache == a->cache);
 
+    max_resized = a->cache->max_resized_saved;
+
     a_i = b_i = merged_i = 0;
     n_original = a->n_original + b->n_original;
     original = g_new(RrImagePic*, n_original);

obt/xml.c

@@ -281,7 +281,7 @@ gboolean obt_xml_load_mem(ObtXmlInst *i,
     xmlResetLastError();
 
     i->doc = xmlParseMemory(data, len);
-    if (i) {
+    if (i->doc) {
         i->root = xmlDocGetRootElement(i->doc);
         if (!i->root) {
             xmlFreeDoc(i->doc);