IO: AddInputCharacters function ignore 0 input. (#3252)

Amend ef13d954 + c8ea0a01 (#2541, #2538, #2815)

imgui.cpp

@@ -1142,17 +1142,21 @@ ImGuiIO::ImGuiIO()
 // - on Windows you can get those using ToAscii+keyboard state, or via the WM_CHAR message
 void ImGuiIO::AddInputCharacter(unsigned int c)
 {
-    InputQueueCharacters.push_back(c > 0 && c <= IM_UNICODE_CODEPOINT_MAX ? (ImWchar)c : IM_UNICODE_CODEPOINT_INVALID);
+    if (c != 0)
+        InputQueueCharacters.push_back(c <= IM_UNICODE_CODEPOINT_MAX ? (ImWchar)c : IM_UNICODE_CODEPOINT_INVALID);
 }
 
 // UTF16 strings use surrogate pairs to encode codepoints >= 0x10000, so
 // we should save the high surrogate.
 void ImGuiIO::AddInputCharacterUTF16(ImWchar16 c)
 {
+    if (c == 0 && InputQueueSurrogate == 0)
+        return;
+
     if ((c & 0xFC00) == 0xD800) // High surrogate, must save
     {
         if (InputQueueSurrogate != 0)
-            InputQueueCharacters.push_back(0xFFFD);
+            InputQueueCharacters.push_back(IM_UNICODE_CODEPOINT_INVALID);
         InputQueueSurrogate = c;
         return;
     }
@@ -1177,7 +1181,7 @@ void ImGuiIO::AddInputCharactersUTF8(const char* utf8_chars)
     {
         unsigned int c = 0;
         utf8_chars += ImTextCharFromUtf8(&c, utf8_chars, NULL);
-        if (c > 0)
+        if (c != 0)
             InputQueueCharacters.push_back((ImWchar)c);
     }
 }