Replace empty throws that "should not happen" with an IllegalStateException.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/csv/trunk@1383569 13f79535-47bb-0310-9956-ffa450edef68

Author: garydgregory

src/main/java/org/apache/commons/csv/CSVFormat.java

@@ -431,11 +431,11 @@ public String format(String... values) {
         StringWriter out = new StringWriter();
         try {
             new CSVPrinter(out, this).println(values);
+            return out.toString().trim();
         } catch (IOException e) {
             // should not happen
-        }
-        
-        return out.toString().trim();
+            throw new IllegalStateException(e);
+        }        
     }
 
     @Override