patch 9.0.1391: "clear" macros are not always used

Problem:    "clear" macros are not always used.
Solution:   Use ALLOC_ONE, VIM_CLEAR, CLEAR_POINTER and CLEAR_FIELD in more
            places. (Yegappan Lakshmanan, closes #12104)
diff --git a/src/os_qnx.c b/src/os_qnx.c
index 4a7b363..d3ebb20 100644
--- a/src/os_qnx.c
+++ b/src/os_qnx.c
@@ -24,7 +24,7 @@
 #if defined(FEAT_GUI_PHOTON)
     PhChannelParms_t parms;
 
-    memset(&parms, 0, sizeof(parms));
+    CLEAR_FIELD(parms);
     parms.flags = Ph_DYNAMIC_BUFFER;
 
     is_photon_available = (PhAttach(NULL, &parms) != NULL) ? TRUE : FALSE;
@@ -124,7 +124,7 @@
 
 	if (text_clip && vim_clip)
 	{
-	    memset(clip_header, 0, sizeof(clip_header));
+	    CLEAR_FIELD(clip_header);
 
 	    STRNCPY(clip_header[0].type, CLIP_TYPE_VIM, 8);
 	    clip_header[0].length = sizeof(vim_clip);