Added @Invariant comments in missing places

Some of the fields for translation that are not required in translation to other languages (as far as I know) do not contain the appropriate comment, this correction adds the required comment.

ShareX.MediaLib/Forms/ImageCombinerForm.resx

@@ -683,6 +683,7 @@
   </data>
   <data name="lblImageCount.Text" xml:space="preserve">
     <value>0</value>
+    <comment>@Invariant</comment>
   </data>
   <data name="lblImageCount.TextAlign" type="System.Drawing.ContentAlignment, System.Drawing">
     <value>TopRight</value>

ShareX.ScreenCaptureLib/Forms/FFmpegOptionsForm.resx

@@ -1,4 +1,4 @@
-<?xml version="1.0" encoding="utf-8"?>
+<?xml version="1.0" encoding="utf-8"?>
 <root>
   <!-- 
     Microsoft ResX Schema 
@@ -133,6 +133,7 @@
   </data>
   <data name="lblx264CRF.Text" xml:space="preserve">
     <value>CRF:</value>
+    <comment>@Invariant</comment>
   </data>
   <data name="&gt;&gt;lblx264CRF.Name" xml:space="preserve">
     <value>lblx264CRF</value>
@@ -597,6 +598,7 @@ Otherwise it can't keep up with recording and a lot of frame drops will happen.<
   </data>
   <data name="btnFFmpegBrowse.Text" xml:space="preserve">
     <value>...</value>
+    <comment>@Invariant</comment>
   </data>
   <data name="&gt;&gt;btnFFmpegBrowse.Name" xml:space="preserve">
     <value>btnFFmpegBrowse</value>

ShareX.ScreenCaptureLib/Forms/ScreenRecordForm.resx

@@ -170,6 +170,7 @@
   </data>
   <data name="lblTimer.Text" xml:space="preserve">
     <value>00:00:00</value>
+    <comment>@Invariant</comment>
   </data>
   <data name="lblTimer.TextAlign" type="System.Drawing.ContentAlignment, System.Drawing">
     <value>MiddleCenter</value>
@@ -314,6 +315,7 @@
   </metadata>
   <data name="niTray.Text" xml:space="preserve">
     <value>ShareX</value>
+    <comment>@Invariant</comment>
   </data>
   <data name="niTray.Visible" type="System.Boolean, mscorlib">
     <value>True</value>