InputText: Amends and tidying up: Fixed undo/redo state corruption when editing buffer in user callback. (#4947, #4949)

imgui.h

@@ -1809,6 +1809,7 @@ struct ImVector
     inline void         resize(int new_size, const T& v)    { if (new_size > Capacity) reserve(_grow_capacity(new_size)); if (new_size > Size) for (int n = Size; n < new_size; n++) memcpy(&Data[n], &v, sizeof(v)); Size = new_size; }
     inline void         shrink(int new_size)                { IM_ASSERT(new_size <= Size); Size = new_size; } // Resize a vector to a smaller size, guaranteed not to cause a reallocation
     inline void         reserve(int new_capacity)           { if (new_capacity <= Capacity) return; T* new_data = (T*)IM_ALLOC((size_t)new_capacity * sizeof(T)); if (Data) { memcpy(new_data, Data, (size_t)Size * sizeof(T)); IM_FREE(Data); } Data = new_data; Capacity = new_capacity; }
+    inline void         reserve_discard(int new_capacity)   { if (new_capacity <= Capacity) return; if (Data) IM_FREE(Data); Data = (T*)IM_ALLOC((size_t)new_capacity * sizeof(T)); Capacity = new_capacity; }
 
     // NB: It is illegal to call push_back/push_front/insert with a reference pointing inside the ImVector data itself! e.g. v.push_back(v[10]) is forbidden.
     inline void         push_back(const T& v)               { if (Size == Capacity) reserve(_grow_capacity(Size + 1)); memcpy(&Data[Size], &v, sizeof(v)); Size++; }