Remove a redundant while-loop condition when reading RFC822-style

header text from a PuTTY key file.

(It's silly to have both while (len > 0) at the top of the loop _and_
an if (len == 0) return in the middle, and in fact the former was the
erroneous one since it would have prohibited a 39-character header,
which I intended to be permitted.)

[originally from svn r9926]

sshpubk.c

@@ -463,7 +463,7 @@ static int read_header(FILE * fp, char *header)
     int len = 39;
     int c;
 
-    while (len > 0) {
+    while (1) {
 	c = fgetc(fp);
 	if (c == '\n' || c == '\r' || c == EOF)
 	    return 0;		       /* failure */