Fix Control+Space not sent to program running in terminal (#16298)

Converts null byte to specific input event, so that it's properly
delivered to the program running in the terminal.

Closes #15939

(cherry picked from commit 8747a39)
Service-Card-Id: 91201444
Service-Version: 1.19

src/host/inputBuffer.cpp

@@ -830,6 +830,17 @@ void InputBuffer::_HandleTerminalInputCallback(const TerminalInput::StringType&
 
         for (const auto& wch : text)
         {
+            if (wch == UNICODE_NULL)
+            {
+                // Convert null byte back to input event with proper control state
+                const auto zeroKey = OneCoreSafeVkKeyScanW(0);
+                uint32_t ctrlState = 0;
+                WI_SetFlagIf(ctrlState, SHIFT_PRESSED, WI_IsFlagSet(zeroKey, 0x100));
+                WI_SetFlagIf(ctrlState, LEFT_CTRL_PRESSED, WI_IsFlagSet(zeroKey, 0x200));
+                WI_SetFlagIf(ctrlState, LEFT_ALT_PRESSED, WI_IsFlagSet(zeroKey, 0x400));
+                _storage.push_back(SynthesizeKeyEvent(true, 1, LOBYTE(zeroKey), 0, wch, ctrlState));
+                continue;
+            }
             _storage.push_back(SynthesizeKeyEvent(true, 1, 0, 0, wch, 0));
         }