Utils: Fix small string

Change-Id: I94b9cd4c282bf57254b52172658135237d4073bd
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/libs/utils/smallstring.h

@@ -464,9 +464,11 @@ public:
 
             reserve(optimalCapacity(newSize));
 
-            std::memcpy(data() + oldSize, temporaryArray, newAppendedStringSize);
+            auto begin = data();
 
-            newEnd = data() + newSize;
+            std::memcpy(begin + oldSize, temporaryArray, newAppendedStringSize);
+
+            newEnd = begin + newSize;
         }
         setSize(newEnd - data());
     }

src/libs/utils/smallstringlayout.h

@@ -281,7 +281,7 @@ struct alignas(16) StringDataLayout<MaximumShortStringDataAreaSize,
 
     constexpr void reset() noexcept
     {
-        pointer = nullptr;
+        pointer = buffer;
         size_ = 0;
         capacity_ = MaximumShortStringDataAreaSize;
     }