internal/gamepaddb: bug fix: platform was not initialized correctly

After 6552ae1, the order of the init
function calls changed, and then the platform was not initialized
correctly.

This change fixes this issue by not relying on an init function to
get the platform.

Closes #2964

internal/gamepaddb/gamepaddb.go

@@ -36,12 +36,9 @@ const (
 	platformIOS
 )
 
-var currentPlatform platform
-
-func init() {
+func currentPlatform() platform {
 	if runtime.GOOS == "windows" {
-		currentPlatform = platformWindows
-		return
+		return platformWindows
 	}
 
 	if runtime.GOOS == "aix" ||
@@ -53,24 +50,22 @@ func init() {
 		runtime.GOOS == "netbsd" ||
 		runtime.GOOS == "openbsd" ||
 		runtime.GOOS == "solaris" {
-		currentPlatform = platformUnix
-		return
+		return platformUnix
 	}
 
 	if runtime.GOOS == "android" {
-		currentPlatform = platformAndroid
-		return
+		return platformAndroid
 	}
 
 	if runtime.GOOS == "ios" {
-		currentPlatform = platformIOS
-		return
+		return platformIOS
 	}
 
 	if runtime.GOOS == "darwin" {
-		currentPlatform = platformMacOS
-		return
+		return platformMacOS
 	}
+
+	return platformUnknown
 }
 
 type mappingType int
@@ -333,7 +328,7 @@ func buttonMappings(id string) map[StandardButton]mapping {
 	if m, ok := gamepadButtonMappings[id]; ok {
 		return m
 	}
-	if currentPlatform == platformAndroid {
+	if currentPlatform() == platformAndroid {
 		if addAndroidDefaultMappings(id) {
 			return gamepadButtonMappings[id]
 		}
@@ -345,7 +340,7 @@ func axisMappings(id string) map[StandardAxis]mapping {
 	if m, ok := gamepadAxisMappings[id]; ok {
 		return m
 	}
-	if currentPlatform == platformAndroid {
+	if currentPlatform() == platformAndroid {
 		if addAndroidDefaultMappings(id) {
 			return gamepadAxisMappings[id]
 		}
@@ -541,7 +536,7 @@ func Update(mappingData []byte) error {
 
 	for s.Scan() {
 		line := s.Text()
-		id, name, buttons, axes, err := parseLine(line, currentPlatform)
+		id, name, buttons, axes, err := parseLine(line, currentPlatform())
 		if err != nil {
 			return err
 		}