scene/surfaceitem: prevent division by zero

If the steady_clock's resolution is very limited, now - m_lastDamage might be zero,
so enforce a minimum time of 10us (or 100'000 fps)

src/scene/surfaceitem.cpp

@@ -8,6 +8,8 @@
 #include "core/pixelgrid.h"
 #include "scene/scene.h"
 
+using namespace std::chrono_literals;
+
 namespace KWin
 {
 
@@ -102,13 +104,13 @@ static QRegion expandRegion(const QRegion &region, const QMargins &padding)
 void SurfaceItem::addDamage(const QRegion &region)
 {
     if (m_lastDamage) {
-        const auto diff = std::chrono::steady_clock::now() - *m_lastDamage;
+        const auto diff = std::max(std::chrono::steady_clock::now() - *m_lastDamage, 10'000ns);
         m_lastDamageTimeDiffs.push_back(diff);
         if (m_lastDamageTimeDiffs.size() > 100) {
             m_lastDamageTimeDiffs.pop_front();
         }
-        const auto average = std::accumulate(m_lastDamageTimeDiffs.begin(), m_lastDamageTimeDiffs.end(), std::chrono::nanoseconds::zero()) / m_lastDamageTimeDiffs.size();
-        m_refreshRate = std::chrono::nanoseconds(1'000'000'000) / average;
+        const auto average = std::accumulate(m_lastDamageTimeDiffs.begin(), m_lastDamageTimeDiffs.end(), 0ns) / m_lastDamageTimeDiffs.size();
+        m_refreshRate = 1'000'000'000ns / average;
     }
     m_lastDamage = std::chrono::steady_clock::now();
     m_damage += region;