Correctly detect missing parameter value.

When parsing URI parameters, the following case was not detected:

  ?param1&param2=value

The absence of a value for param1 was missed because the code would look
for the '=' character in the next parameter (as if there was a single
parameter named 'param1&param2').

Fix that by checking that the '=' delimiter comes before the next '&'
delimiter, if any.

src/secretcfg.c

@@ -201,11 +201,12 @@ parse_parameter(const char **uri, gfsec_share_t *share)
     if ( **uri == '\0' )
         return 0;   /* Silently ignore terminal delimiter. */
 
-    if ( ! (eq = strchr(*uri, '=')) )
-        return GFSEC_ERR_CONFIG_INVALID_URI;
+    amp = strchrnul(*uri, '&');
+    if ( ! (eq = strchr(*uri, '=')) || amp < eq )
+        return GFSEC_ERR_CONFIG_INVALID_URI;    /* Missing value. */
 
     if ( strncmp(*uri, "share", eq - *uri) == 0 ) {
-        amp = strchrnul(++eq, '&');
+        eq += 1;
         if ( strncmp(eq, "no", amp - eq) == 0 )
             share->number = GFSEC_SHARE_NUMBER_FULL;
         else if ( strncmp(eq, "full", amp - eq) == 0 )
@@ -215,7 +216,7 @@ parse_parameter(const char **uri, gfsec_share_t *share)
         *uri = amp;
     }
     else if ( strncmp(*uri, "sha256", eq - *uri) == 0 ) {
-        amp = strchrnul(++eq, '&');
+        eq += 1;
         rc = parse_sha256(eq, amp - eq, &(share->hash));
         *uri = amp;
     }

tests/t-parseuri.c

@@ -69,11 +69,15 @@ struct test tests[] = {
     /* Several parameters. */
     { "file:///path/to/share.123?param1=val1&param2=val2&param3=val3",
         0, GFSEC_SCHEME_FILE, "", "/path/to/share.123", 123, 0 },
+    { "file:///path/to/share.123?param1=val&share=no&param3=val3",
+        0, GFSEC_SCHEME_FILE, "", "/path/to/share.123", 0, 1 },
 
     /* Parameter with no value. */
     { "file:///path/to/share.123?param", GFSEC_ERR_CONFIG_INVALID_URI },
     { "file:///path/to/share.123?param1=val1&param2",
         GFSEC_ERR_CONFIG_INVALID_URI },
+    { "file:///path/to/share.123?param1=val1&param2&param3=val",
+        GFSEC_ERR_CONFIG_INVALID_URI },
 
     /* Parameter with empty value. */
     { "file:///path/to/share.123?param=",