Consistent variable names for feature checks

 As pointed out in GitHub, the variables "CURL_HAS_PARALLEL" and
 "CURL_NO_CLOBBER" were a bit confusing as they did not represent
 boolean values like the other "HAS"-type variables.

 Thanks to Ilya Sher for the suggestion.

 Closes: #60

Author: samueloph

wcurl

@@ -186,19 +186,19 @@ exec_curl()
     curl_version_major=$(echo "$curl_version" | cut -f1 -d.)
     curl_version_minor=$(echo "$curl_version" | cut -f2 -d.)
 
-    CURL_HAS_NO_CLOBBER=""
-    CURL_HAS_PARALLEL=""
+    CURL_NO_CLOBBER=""
+    CURL_PARALLEL=""
     # --no-clobber is only supported since 7.83.0.
     # --parallel is only supported since 7.66.0.
     if [ "${curl_version_major}" -ge 8 ]; then
-        CURL_HAS_NO_CLOBBER="--no-clobber"
-        CURL_HAS_PARALLEL="--parallel"
+        CURL_NO_CLOBBER="--no-clobber"
+        CURL_PARALLEL="--parallel"
     elif [ "${curl_version_major}" -eq 7 ]; then
         if [ "${curl_version_minor}" -ge 83 ]; then
-            CURL_HAS_NO_CLOBBER="--no-clobber"
+            CURL_NO_CLOBBER="--no-clobber"
         fi
         if [ "${curl_version_minor}" -ge 66 ]; then
-            CURL_HAS_PARALLEL="--parallel"
+            CURL_PARALLEL="--parallel"
         fi
     fi
 
@@ -207,9 +207,8 @@ exec_curl()
     # shellcheck disable=SC2086
     set -- $URLS
 
-    if [ "$#" -gt 1 ]; then
-        CURL_PARALLEL="$CURL_HAS_PARALLEL"
-    else
+    # If there are less than two URLs, don't set the parallel flag.
+    if [ "$#" -lt 2 ]; then
         CURL_PARALLEL=""
     fi
 
@@ -231,7 +230,7 @@ exec_curl()
             [ -z "${OUTPUT_PATH}" ] && OUTPUT_PATH=index.html
         fi
         # shellcheck disable=SC2086
-        set -- "$@" ${NEXT_PARAMETER} ${PER_URL_PARAMETERS} ${CURL_HAS_NO_CLOBBER} --output "${OUTPUT_PATH}" ${CURL_OPTIONS} "${url}"
+        set -- "$@" ${NEXT_PARAMETER} ${PER_URL_PARAMETERS} ${CURL_NO_CLOBBER} --output "${OUTPUT_PATH}" ${CURL_OPTIONS} "${url}"
         NEXT_PARAMETER="--next"
     done