fix: address PR #98 review feedback

- check-cwe134.sh: match gchar* in addition to char* in variadic pattern
- rosterwin.c: merge duplicated if/else into single condition
- omemo.c: remove unnecessary scope block and goto, use early return

check-cwe134.sh

@@ -75,7 +75,7 @@ KNOWN_RE=$(IFS="|"; echo "${REQUIRED_ATTRIBUTED[*]}")
 # Find variadic declarations with a const char* / gchar* parameter followed by ...)
 # that do NOT have a format attribute on the preceding line
 NEW_ISSUES=$(grep -B1 -rn --include="*.h" \
-    -E '(const g?char)\s*\*.*,\s*\.\.\.\)' "$DIR" 2>/dev/null \
+    'const g\?char\s*\*.*,\s*\.\.\.)' "$DIR" 2>/dev/null \
     | awk '
         /format\(printf|G_GNUC_PRINTF/ { skip=1; next }
         /const g?char.*,.*\.\.\.\)/ {