Fixed log file issues on a freshly installed Friendica.

* Check to see if log file exists.
* After trying to open it, check to see if it went ok.
* So, check to see if the file size != 0 (fread error with size = 0)

mod/admin.php

@@ -635,13 +635,25 @@ function admin_page_logs(&$a){
 	$t = get_markup_template("admin_logs.tpl");
 
 	$f = get_config('system','logfile');
-	$size = filesize($f);
-	if($size > 5000000 || $size < 0)
-		$size = 5000000;
 
 	$data = '';
+
+	if(!file_exists($f)) {
+		$data = t("Error trying to open <strong>$f</strong> log file.\r\n<br/>Check to see if file $f exist and is 
+readable.");
+	}
+	else {
 		$fp = fopen($f, 'r');
-	if($fp) {
+		if(!$fp) {
+			$data = t("Couldn't open <strong>$f</strong> log file.\r\n<br/>Check to see if file $f is readable.");
+		}
+		else {
+			$fstat = fstat($fp);
+			$size = $fstat['size'];
+			if($size != 0)
+			{
+				if($size > 5000000 || $size < 0)
+					$size = 5000000;
 				$seek = fseek($fp,0-$size,SEEK_END);
 				if($seek === 0) {
 					fgets($fp); // throw away the first partial line
@@ -649,9 +661,10 @@ function admin_page_logs(&$a){
 					while(! feof($fp))
 						$data .= escape_tags(fread($fp,4096));
 				}
+			}
 			fclose($fp);
 		}
-
+	}			
 
 	return replace_macros($t, array(
 		'$title' => t('Administration'),