fixes crash in sign up activity in api 21 and 22 (#5311)

* fixes crash in sign up activity

* javadoc comments added

app/src/main/java/fr/free/nrw/commons/auth/SignupActivity.java

@@ -1,5 +1,7 @@
 package fr.free.nrw.commons.auth;
 
+import android.content.res.Configuration;
+import android.os.Build;
 import android.os.Bundle;
 import android.webkit.WebSettings;
 import android.webkit.WebView;
@@ -61,4 +63,20 @@ public void onBackPressed() {
             super.onBackPressed();
         }
     }
+
+    /**
+     * Known bug in androidx.appcompat library version 1.1.0 being tracked here
+     * https://issuetracker.google.com/issues/141132133
+     * App tries to put light/dark theme to webview and crashes in the process
+     * This code tries to prevent applying the theme when sdk is between api 21 to 25
+     * @param overrideConfiguration
+     */
+    @Override
+    public void applyOverrideConfiguration(final Configuration overrideConfiguration) {
+        if (Build.VERSION.SDK_INT <= 25 &&
+            (getResources().getConfiguration().uiMode == getApplicationContext().getResources().getConfiguration().uiMode)) {
+            return;
+        }
+        super.applyOverrideConfiguration(overrideConfiguration);
+    }
 }