pcsx2|gsdx: avoid potential null deferencement

pcsx2/CDVD/zlib_indexed.h

@@ -303,6 +303,11 @@ local int build_index(FILE *in, PX_off_t span, struct access **built)
         }
     } while (ret != Z_STREAM_END);
 
+    if (index == NULL) {
+        // Could happen if the start of the stream in Z_STREAM_END
+        return 0;
+    }
+
     /* clean up and return index (release unused entries in list) */
     (void)inflateEnd(&strm);
     index->list = (Point*)realloc(index->list, sizeof(struct point) * index->have);

plugins/GSdx/GSRendererHW.cpp

@@ -463,6 +463,7 @@ void GSRendererHW::Draw()
 		{
 			s = format("%05d_f%lld_rz0_%05x_%d.bmp", s_n, frame, context->ZBUF.Block(), context->ZBUF.PSM);
 
+			if (ds_tex)
 				ds_tex->Save(root_hw+s);
 		}