reorder "I;16" endianness check

Co-authored-by: Andrew Murray <[email protected]>

Author: Yay295

src/_imaging.c

@@ -1574,17 +1574,16 @@ if (PySequence_Check(op)) { \
             // 0 = none, 1 = little, 2 = big
             int endian = 0;
             if (strncmp(image->mode, "I;16", 4) == 0) {
-                if (strcmp(image->mode, "I;16") == 0 || strcmp(image->mode, "I;16L") == 0) {
-                    endian = 1;
-                } else if (strcmp(image->mode, "I;16B") == 0) {
-                    endian = 2;
-                } else {
-                    // native endianness
+                if (strcmp(image->mode, "I;16N") == 0) {
 #ifdef WORDS_BIGENDIAN
                     endian = 2;
 #else
                     endian = 1;
 #endif
+                } else if (strcmp(image->mode, "I;16B") == 0) {
+                    endian = 2;
+                } else {
+                    endian = 1;
                 }
             }
             double value;