From 02599356a09a69b7c1f49851d3f424fcfa4a5651 Mon Sep 17 00:00:00 2001
From: Martin Dobias <wonder.sk@gmail.com>
Date: Tue, 13 Sep 2016 00:37:01 +0800
Subject: [PATCH] Fix crash on QMap iteration in Qt5

---
 src/providers/wms/qgswmscapabilities.cpp | 22 +++++++++++++++++++---
 1 file changed, 19 insertions(+), 3 deletions(-)

diff --git a/src/providers/wms/qgswmscapabilities.cpp b/src/providers/wms/qgswmscapabilities.cpp
index fc3e1a90381..c1f8aca01c6 100644
--- a/src/providers/wms/qgswmscapabilities.cpp
+++ b/src/providers/wms/qgswmscapabilities.cpp
@@ -2157,9 +2157,25 @@ const QgsWmtsTileMatrix *QgsWmtsTileMatrixSet::findOtherResolution( double tres,
   QMap<double, QgsWmtsTileMatrix>::const_iterator it = tileMatrices.constFind( tres );
   if ( it == tileMatrices.constEnd() )
     return nullptr;
-  it += offset;
-  if ( it == tileMatrices.constEnd() )
-    return nullptr;
+  while ( 1 )
+  {
+    if ( offset > 0 )
+    {
+      ++it;
+      --offset;
+    }
+    else if ( offset < 0 )
+    {
+      if ( it == tileMatrices.constBegin() )
+        return nullptr;
+      --it;
+      ++offset;
+    }
+    else
+      break;
 
+    if ( it == tileMatrices.constEnd() )
+      return nullptr;
+  }
   return &it.value();
 }