PDFBOX-5660: fix typo, as suggested by Valery Bokov; improve javadoc; closes #286

git-svn-id: https://svn.apache.org/repos/asf/pdfbox/trunk@1929070 13f79535-47bb-0310-9956-ffa450edef68

Author: THausherr

io/src/main/java/org/apache/pdfbox/io/NonSeekableRandomAccessReadInputStream.java

@@ -259,7 +259,7 @@ else if (bufferBytes[LAST] > 0)
         else
         {
             // there aren't enough bytes left in the buffers to perform the rewind operation
-            throw new IOException("not enough bytes available to perfomr the rewind operation");
+            throw new IOException("not enough bytes available to perform the rewind operation");
         }
     }