fix: handle error when defining a nil reference (#2717)

# Summary

That PR helped to solve issue #2715 

This issue arises on the iOS platform because
`NSMutableDictionary<NSString *, RNSVGNode *>` does not allow nil keys
or values. On Android, however, the `Map<String, VirtualView>`
implementation does allow null keys, which prevents this issue from
occurring there.

To address the iOS issue, we handle nil values for elements such as
`clipPaths, templates, painters, markers, masks, and filters`. Managing
`nil` values in `RNSVGSvgView.mm` is practical because the `define*`
method is used in multiple locations.

---------

Co-authored-by: Jakub Grzywacz <kontakt@jakubgrzywacz.pl>
Co-authored-by: Jakub Grzywacz <jakub.grzywacz@swmansion.com>

Author: bohdanprog

apple/Elements/RNSVGSvgView.mm

@@ -402,6 +402,9 @@ - (void)reactSetInheritedBackgroundColor:(RNSVGColor *)inheritedBackgroundColor
 
 - (void)defineClipPath:(__kindof RNSVGNode *)clipPath clipPathName:(NSString *)clipPathName
 {
+  if (!clipPathName) {
+    return;
+  }
   if (!_clipPaths) {
     _clipPaths = [[NSMutableDictionary alloc] init];
   }
@@ -415,6 +418,9 @@ - (RNSVGNode *)getDefinedClipPath:(NSString *)clipPathName
 
 - (void)defineTemplate:(RNSVGNode *)definedTemplate templateName:(NSString *)templateName
 {
+  if (!templateName) {
+    return;
+  }
   if (!_templates) {
     _templates = [[NSMutableDictionary alloc] init];
   }
@@ -428,6 +434,9 @@ - (RNSVGNode *)getDefinedTemplate:(NSString *)templateName
 
 - (void)definePainter:(RNSVGPainter *)painter painterName:(NSString *)painterName
 {
+  if (!painterName) {
+    return;
+  }
   if (!_painters) {
     _painters = [[NSMutableDictionary alloc] init];
   }
@@ -441,6 +450,9 @@ - (RNSVGPainter *)getDefinedPainter:(NSString *)painterName
 
 - (void)defineMarker:(RNSVGMarker *)marker markerName:(NSString *)markerName
 {
+  if (!markerName) {
+    return;
+  }
   if (!_markers) {
     _markers = [[NSMutableDictionary alloc] init];
   }
@@ -454,6 +466,9 @@ - (RNSVGMarker *)getDefinedMarker:(NSString *)markerName
 
 - (void)defineMask:(RNSVGMask *)mask maskName:(NSString *)maskName
 {
+  if (!maskName) {
+    return;
+  }
   if (!_masks) {
     _masks = [[NSMutableDictionary alloc] init];
   }
@@ -467,6 +482,9 @@ - (RNSVGMask *)getDefinedMask:(NSString *)maskName
 
 - (void)defineFilter:(RNSVGFilter *)filter filterName:(NSString *)filterName
 {
+  if (!filterName) {
+    return;
+  }
   if (!_filters) {
     _filters = [[NSMutableDictionary alloc] init];
   }