Fix validation of diff mode

Remove bad else statement which was included accidentally and which
caused the diff mode validation to be executed only for images.

Change-Id: I6f2a3995e483fb7d8498afbf7bc227f40a87be04
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>

src/main/java/com/googlesource/gerrit/plugins/xdocs/XDocServlet.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/xdocs/XDocServlet.java b/src/main/java/com/googlesource/gerrit/plugins/xdocs/XDocServlet.java
index d180c64..28d30f7 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/xdocs/XDocServlet.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/xdocs/XDocServlet.java
@@ -140,7 +140,7 @@
       }
       if (formatter == null && !isSafeImage(mimeType)) {
         throw new ResourceNotFoundException();
-      } else if (isSafeImage(mimeType))
+      }
 
       validateDiffMode(key, formatter, mimeType);