Fixed RS274X image rotation parsing.

If the image was being rotated by a valid amount but not 270 degrees due to the if statements it would already report that there was an invalid value.

Also due to the strnicmp only checking the first 2 characters which was valid for 0* but not the rest of the numbers, some values would be able to work that shouldn't

gerbview/rs274x.cpp

@@ -434,11 +434,11 @@ bool GERBER_IMAGE::ExecuteRS274XCommand( int       command,
     case IMAGE_ROTATION:    // command IR0* or IR90* or IR180* or IR270*
         if( strnicmp( text, "0*", 2 ) == 0 )
             m_ImageRotation = 0;
-        if( strnicmp( text, "90*", 2 ) == 0 )
+        else if( strnicmp( text, "90*", 3 ) == 0 )
             m_ImageRotation = 90;
-        if( strnicmp( text, "180*", 2 ) == 0 )
+        else if( strnicmp( text, "180*", 4 ) == 0 )
             m_ImageRotation = 180;
-        if( strnicmp( text, "270*", 2 ) == 0 )
+        else if( strnicmp( text, "270*", 4 ) == 0 )
             m_ImageRotation = 270;
         else
             ReportMessage( _( "RS274X: Command \"IR\" rotation value not allowed" ) );