Photoviewer: Fix warnings flood

Accept https and check for the match of the regexp, fixing:

rc:/PhotoViewerCore/script/script.mjs:61: TypeError: Cannot read property '1' of null
qrc:/PhotoViewerCore/script/script.mjs:61: TypeError: Cannot read property '1' of null
qrc:/PhotoViewerCore/script/script.mjs:61: TypeError: Cannot read property '1' of null
qrc:/PhotoViewerCore/script/script.mjs:61: TypeError: Cannot read property '1' of null
qrc:/PhotoViewerCore/script/script.mjs:61: TypeError: Cannot read property '1' of null
qrc:/PhotoViewerCore/script/script.mjs:61: TypeError: Cannot read property '1' of null

Fixes: QTBUG-75255
Change-Id: I3c447830874d504213276b8064abcf3cef1f72ec
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>
Reviewed-by: Paul Wicking <paul.wicking@qt.io>

examples/demos/photoviewer/PhotoViewerCore/script/script.mjs

@@ -57,8 +57,9 @@ export function getHeight(string) {
 }
 
 export function getImagePath(string) {
-    var pattern = /src=\"http:\/\/(\S+)\"/
-    return (string.match(pattern))[1]
+    var pattern = /src=\"https?:\/\/(\S+)\"/
+    var match = string.match(pattern)
+    return match ? match[1] : ""
 }
 
 export function calculateScale(width, height, cellSize) {