InputMapping: fix OOB access, reject DEVICE_ID_ANY mappings

FromConfigString() indexed parts[0]/parts[1] from SplitString() with
no check that at least 2 parts were produced - a malformed/truncated
line in a hand-edited controls.ini (no '-') was an OOB vector access.

Separately, DEVICE_ID_ANY (-1) didn't round-trip correctly:
ToConfigString() formats it as e.g. "-1-5", but splitting that on '-'
produces "", "1", "5" instead of "-1", "5" - deviceId decoded to 0 and
keyCode to 1 instead of 5. Rather than special-casing the negative
sign to make it round-trip, just reject DEVICE_ID_ANY mappings
outright - it's not something we want to support, and the whole ANY
concept is likely going away. Preserves the existing (tested) behavior
of tolerating a MultiInputMapping string and parsing just its first
mapping, via atoi()'s stop-at-first-non-digit behavior.

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01L4QAoxV2KY7ek4PcZw3WvY

Common/Input/InputState.cpp

@@ -3,6 +3,7 @@
 
 #include "Common/Input/InputState.h"
 #include "Common/Input/KeyCodes.h"
+#include "Common/Log.h"
 #include "Common/StringUtils.h"
 
 const char *GetDeviceName(int deviceId) {
@@ -90,9 +91,25 @@ int GetAnalogYDirection(InputDeviceID deviceId) {
 
 // NOTE: Changing the format of FromConfigString/ToConfigString breaks controls.ini backwards compatibility.
 InputMapping InputMapping::FromConfigString(const std::string_view str) {
+	// DEVICE_ID_ANY (-1) is not a mapping we want to support (and the ANY concept is likely
+	// going away entirely), so reject it outright instead of trying to round-trip a negative
+	// device ID through the '-'-separated format.
+	if (str.size() >= 2 && str[0] == '-' && str[1] == '1') {
+		ERROR_LOG(Log::System, "Rejecting DEVICE_ID_ANY InputMapping config string: '%.*s'", (int)str.size(), str.data());
+		return InputMapping();
+	}
+
 	std::vector<std::string_view> parts;
 	SplitString(str, '-', parts);
+	if (parts.size() < 2) {
+		// Malformed entry, e.g. a corrupted/hand-edited controls.ini line.
+		ERROR_LOG(Log::System, "Bad InputMapping config string: '%.*s'", (int)str.size(), str.data());
+		return InputMapping();
+	}
+
 	// We only convert to std::string here to add null terminators for atoi.
+	// Note: atoi() stopping at the first non-digit character is relied upon elsewhere
+	// to let this parse just the first mapping out of a MultiInputMapping string.
 	InputDeviceID deviceId = (InputDeviceID)(atoi(std::string(parts[0]).c_str()));
 	InputKeyCode keyCode = (InputKeyCode)atoi(std::string(parts[1]).c_str());