misc: ISSPACE() => ISBLANK()

Instances of ISSPACE() use that should rather use ISBLANK(). I think
somewhat carelessly used because it sounds as if it checks for space or
whitespace, but also includes %0a to %0d.

For parsing purposes, we should only accept what we must and not be
overly liberal. It leads to surprises and surprises lead to bad things.

Closes #9432

lib/content_encoding.c

@@ -1044,7 +1044,7 @@ CURLcode Curl_build_unencoding_stack(struct Curl_easy *data,
     size_t namelen;
 
     /* Parse a single encoding name. */
-    while(ISSPACE(*enclist) || *enclist == ',')
+    while(ISBLANK(*enclist) || *enclist == ',')
       enclist++;
 
     name = enclist;