ImGuiInputTextCallback: NULL buffer when ReadOnly

[actondev]

Version: v1.85
Branch: master

When passing the ImGuiInputTextFlags_ReadOnly to InputText, the callback_data.Buf is null. Meanwhile, BufTextLen is (correctly) the text length.

Something like

                     callback_data.EventKey = event_key;
-                    callback_data.Buf = state->TextA.Data;
+                    callback_data.Buf = state->TextAIsValid ? state->TextA.Data : state->InitialTextA.Data;
                     callback_data.BufTextLen = state->CurLenA;

seems to be semantically correct, but then

IM_ASSERT(callback_data.Buf == state->TextA.Data);

will fail

[ocornut]

Thank you! Pushed a fix 5ac25e7