Add precision about exploitability in ChangeLog

Also fix some whitespace while at it.
diff --git a/library/rsa.c b/library/rsa.c
index 3cb92f4..9150e87 100644
--- a/library/rsa.c
+++ b/library/rsa.c
@@ -595,7 +595,7 @@
         return( MBEDTLS_ERR_RSA_BAD_INPUT_DATA );
 
     olen = ctx->len;
-    
+
     // first comparison checks for overflow
     if( ilen + 11 < ilen || olen < ilen + 11 )
         return( MBEDTLS_ERR_RSA_BAD_INPUT_DATA );