fix: stack buffer overflow in PreviewWindow::drawTime (#1945)

radio/src/gui/colorlcd/preview_window.h

@@ -282,15 +282,14 @@ class PreviewWindow : public FormGroup
   {
     // time on top bar
     struct gtm t;
-    char str[10];
-    char str1[20];
+    char str[16];
     const char *const STR_MONTHS[] = TR_MONTHS;
 
     gettime(&t);
-    sprintf(str, "%d %s\n", t.tm_mday, STR_MONTHS[t.tm_mon]);
-
-    getTimerString(str1, getValue(MIXSRC_TX_TIME));
-    strcat(str, str1);
+    int s = snprintf(str, sizeof(str), "%d %s\n", t.tm_mday, STR_MONTHS[t.tm_mon]);
+    if (s > 0 && s < sizeof(str) - 6 /* 00:00\0 */) {
+      getTimerString(str + s, getValue(MIXSRC_TX_TIME));
+    }
     dc->drawText(rect.w - 40, 5, str, COLOR_THEME_PRIMARY2 | FONT(XS));
   }
 
@@ -334,4 +333,4 @@ class PreviewWindow : public FormGroup
   tmr10ms_t ticks;
 };
 
-#endif
+#endif