lib/utils_base.c: if asprintf fails, string is undefined

if asprintf fails, string content becomes invalid. we need
to check if it ran OK by checking the returned value.

in case of fail, asprintf returns -1, otherwise the number
of writen bytes is returned.

also, on ubuntu 13.10 i've receiving a lot of warnings:

"warning: ignoring return value of ‘asprintf’"

this patches fixes some of them

Signed-off-by: Ricardo Maraschini <ricardo.maraschini@gmail.com>
---
Closes #1227

lib/utils_base.c

@@ -446,6 +446,7 @@ void np_enable_state(char *keyname, int expected_data_version) {
 	char *temp_filename = NULL;
 	char *temp_keyname = NULL;
 	char *p=NULL;
+	int ret;
 
 	if(this_monitoring_plugin==NULL)
 		die(STATE_UNKNOWN, _("This requires np_init to be called"));
@@ -476,9 +477,13 @@ void np_enable_state(char *keyname, int expected_data_version) {
 	this_state->state_data=NULL;
 
 	/* Calculate filename */
-	asprintf(&temp_filename, "%s/%lu/%s/%s",
+	ret = asprintf(&temp_filename, "%s/%lu/%s/%s",
 	    _np_state_calculate_location_prefix(), (unsigned long)geteuid(),
 	    this_monitoring_plugin->plugin_name, this_state->name);
+	if (ret < 0)
+		die(STATE_UNKNOWN, _("Cannot allocate memory: %s"),
+		    strerror(errno));
+
 	this_state->_filename=temp_filename;
 
 	this_monitoring_plugin->state = this_state;
@@ -614,8 +619,8 @@ void np_state_write_string(time_t data_time, char *data_string) {
 	
 	/* If file doesn't currently exist, create directories */
 	if(access(this_monitoring_plugin->state->_filename,F_OK)!=0) {
-		asprintf(&directories, "%s", this_monitoring_plugin->state->_filename);
-		if(directories==NULL)
+		result = asprintf(&directories, "%s", this_monitoring_plugin->state->_filename);
+		if(result < 0)
 			die(STATE_UNKNOWN, _("Cannot allocate memory: %s"),
 			    strerror(errno));
 
@@ -633,8 +638,8 @@ void np_state_write_string(time_t data_time, char *data_string) {
 		np_free(directories);
 	}
 
-	asprintf(&temp_file,"%s.XXXXXX",this_monitoring_plugin->state->_filename);
-	if(temp_file==NULL)
+	result = asprintf(&temp_file,"%s.XXXXXX",this_monitoring_plugin->state->_filename);
+	if(result < 0)
 		die(STATE_UNKNOWN, _("Cannot allocate memory: %s"),
 		    strerror(errno));