better bugfix for seven-seg-reloaded

* only reject invalid ranges when array access will be actually performed
* fixed another stupid pointer arithmetic error

Hint: I AM NOT THE MAINTAINER of this usermod. I'm just fixing an obvious coding error without knowing what the usermod really does.

Author: softhack007

usermods/seven_segment_display_reloaded/usermod_seven_segment_reloaded.h

@@ -165,7 +165,7 @@ class UsermodSSDR : public Usermod {
   void _showElements(String *map, int timevar, bool isColon, bool removeZero
 
 ) {
-    if (!(*map).equals("") && !(*map) == NULL) {
+    if ((map != nullptr) && (*map != nullptr) && !(*map).equals("")) {
       int length = String(timevar).length();
       bool addZero = false;
       if (length == 1) {
@@ -237,12 +237,12 @@ class UsermodSSDR : public Usermod {
 
   void _setLeds(int lednr, int lastSeenLedNr, bool range, int countSegments, int number, bool colon) {
     if ((lednr < 0) || (lednr >= umSSDRLength)) return;                                   // prevent array bounds violation
-    if ((number < 0) || (countSegments < 0) || (lastSeenLedNr <0)) return; // prevent array out of range access
 
+    if (!(colon && umSSDRColonblink) && ((number < 0) || (countSegments < 0))) return;
     if ((colon && umSSDRColonblink) || umSSDRNumbers[number][countSegments]) {
 
       if (range) {
-        for(int i = lastSeenLedNr; i <= lednr; i++) {
+        for(int i = max(0, lastSeenLedNr); i <= lednr; i++) {
           umSSDRMask[i] = true;
         }
       } else {