reports: Convert user time to database time

'strtotime' uses local timezone without taking into consideration the user's
timezone. This pull requests simply makes sure user's entered timeframe
range is converted to db time before it's used in a query.

include/class.report.php

@@ -35,13 +35,19 @@ class OverviewReport {
         $start = $this->start ?: 'last month';
         $stop = $this->end ?: 'now';
 
-        $start = strtotime($start);
-
-        if (substr($stop, 0, 1) == '+')
-            $stop = strftime('%Y-%m-%d ', $start) . $stop;
+        // Convert user time to db time
+        $start = Misc::dbtime($start);
+        // Stop time can be relative.
+        if ($stop[0] == '+') {
+            // $start time + time(X days)
+            $now = time();
+            $stop = $start + (strtotime($stop, $now)-$now);
+        } else {
+            $stop = Misc::dbtime($stop);
+        }
 
         $start = 'FROM_UNIXTIME('.$start.')';
-        $stop = 'FROM_UNIXTIME('.strtotime($stop).')';
+        $stop = 'FROM_UNIXTIME('.$stop.')';
 
         return array($start, $stop);
     }

include/staff/dashboard.inc.php

@@ -18,8 +18,10 @@ $plots = $report->getPlotData();
             <?php echo csrf_token(); ?>
             <label>
                 <?php echo __( 'Report timeframe'); ?>:
-                <input type="text" class="dp input-medium search-query" name="start" placeholder="<?php echo __('Last month');?>"i
-                    value="<?php echo Format::htmlchars($_POST['start']); ?>" />
+                <input type="text" class="dp input-medium search-query"
+                    name="start" placeholder="<?php echo __('Last month');?>"i
+                    value="<?php echo $_POST['start'] ?
+                    Format::htmlchars($_POST['start']) : ''; ?>" />
             </label>
             <label>
                 <?php echo __( 'period');?>: