qbsp: make ValueForKey return empty string if key not found

Less error prone as it's usually followed by a strn?cmp or something.
Callers that were relying on null checks updated.

Signed-off-by: Kevin Shanahan <kmshanah@disenchant.net>

qbsp/brush.c

@@ -310,7 +310,7 @@ FindTargetEntity(const char *target)
 
     for (i = 0, ent = map.entities; i < map.numentities; i++, ent++) {
 	name = ValueForKey(ent, "targetname");
-	if (name && !strcasecmp(target, name))
+	if (!strcasecmp(target, name))
 	    return ent;
     }
 
@@ -332,7 +332,7 @@ FixRotateOrigin(mapentity_t *ent)
     char value[20];
 
     search = ValueForKey(ent, "target");
-    if (search)
+    if (search[0])
 	target = FindTargetEntity(search);
 
     if (target) {

qbsp/map.c

@@ -663,7 +663,7 @@ ValueForKey(const mapentity_t *ent, const char *key)
 	if (!strcmp(ep->key, key))
 	    return ep->value;
 
-    return NULL;
+    return "";
 }
 
 

qbsp/qbsp.c

@@ -236,15 +236,15 @@ ProcessFile(void)
     }
 
     wadstring = ValueForKey(pWorldEnt, "_wad");
-    if (!wadstring)
+    if (!wadstring[0])
 	wadstring = ValueForKey(pWorldEnt, "wad");
-    if (!wadstring)
+    if (!wadstring[0])
 	Message(msgWarning, warnNoWadKey);
     else
 	numwads = WADList_Init(&wads, wadstring);
 
     if (!numwads) {
-	if (wadstring)
+	if (wadstring[0])
 	    Message(msgWarning, warnNoValidWads);
 	/* Try the default wad name */
 	defaultwad = AllocMem(OTHER, strlen(options.szMapName) + 5, false);