Refactor getSignatureNavState for robustness

Updated `getSignatureNavState` to handle cases where the global signature list (`_allSignatures`) is unavailable or empty by introducing an early return with a default state.

Revised the logic to calculate `total`, `signed`, and `unsigned` using the global signature list, simplifying the `currentIndex` calculation to use the `signed` count. Updated `canGoPrev` and `canGoNext` to reflect the presence of signed or unsigned signatures.

Removed outdated logic relying on `signatureButtons` and added Turkish comments to clarify the new implementation.

EnvelopeGenerator.ReceiverUI/wwwroot/js/pdf-viewer.js

@@ -462,23 +462,30 @@ window.pdfViewer = {
      * @returns {object} { total, signed, unsigned, currentIndex, canGoPrev, canGoNext }
      */
     getSignatureNavState() {
-        const total = this.signatureButtons.length + this.appliedSignatures.length;
-        const signed = this.appliedSignatures.length;
-        const unsigned = this.signatureButtons.length;
-        
-        // Find index of first unsigned signature button (if any)
-        let currentIndex = -1;
-        if (unsigned > 0) {
-            currentIndex = signed; // 0-based index of next signature to sign
+        // Global imza listesi yoksa bo? state dön
+        if (!this._allSignatures || this._allSignatures.length === 0) {
+            return {
+                total: 0,
+                signed: 0,
+                unsigned: 0,
+                currentIndex: -1,
+                canGoPrev: false,
+                canGoNext: false
+            };
         }
         
+        // TÜM sayfalardaki imzalar? say (database'den gelen global liste)
+        const total = this._allSignatures.length;           // Global: Toplam imza say?s?
+        const signed = this.appliedSignatures.length;       // ?mzalananlar
+        const unsigned = total - signed;                    // Hesaplanan: ?mzalanmayanlar
+        
         return {
             total: total,
             signed: signed,
             unsigned: unsigned,
-            currentIndex: currentIndex,
-            canGoPrev: signed > 0,  // Can go to previous applied signature
-            canGoNext: unsigned > 0  // Can go to next unsigned signature
+            currentIndex: signed,           // Sonraki imzan?n index'i
+            canGoPrev: signed > 0,          // En az 1 imza uygulanm?? m??
+            canGoNext: unsigned > 0         // Hala imzalanmam?? var m??
         };
     },