Simplify jpeg check to first 3 bytes

refs: https://bitbucket.org/wez/atomicparsley/issues/48/jpeg-image-test-requires-jfif-exif-data
refs: https://bitbucket.org/wez/atomicparsley/issues/63

Author: wez

src/id3v2defs.h

@@ -557,8 +557,7 @@ ID3v2FieldDefinition FrameTypeConstructionList[] = {
 
 // used to determine mimetype for APIC image writing
 ImageFileFormatDefinition ImageList[] = {
-    {"image/jpeg", ".jpg", 4, "\xFF\xD8\xFF\xE0"},
-    {"image/jpeg", ".jpg", 4, "\xFF\xD8\xFF\xE1"},
+    {"image/jpeg", ".jpg", 3, "\xFF\xD8\xFF"},
     {"image/png", ".png", 8, "\x89\x50\x4E\x47\x0D\x0A\x1A\x0A"},
     {"image/pdf", ".pdf", 7, "%PDF-1."},
     {"image/jp2",

src/metalist.cpp

@@ -305,8 +305,7 @@ void APar_ExtractAAC_Artwork(short this_atom_num,
 
   if (memcmp(art_payload, "\x89\x50\x4E\x47\x0D\x0A\x1A\x0A", 8) == 0) {
     strcpy(suffix, ".png");
-  } else if (memcmp(art_payload, "\xFF\xD8\xFF\xE0", 4) == 0 ||
-             memcmp(art_payload, "\xFF\xD8\xFF\xE1", 4) == 0) {
+  } else if (memcmp(art_payload, "\xFF\xD8\xFF", 3) == 0) {
     strcpy(suffix, ".jpg");
   }
 

src/nsimage.mm

@@ -38,7 +38,7 @@ void DetermineType(const char *picfilePath) {
 	if (memcmp(picHeader, "\x89\x50\x4E\x47\x0D\x0A\x1A\x0A", 8) == 0) {
 				isPNG=true;
 				isJPEG=false;
-	} else if (memcmp(picHeader, "\xFF\xD8\xFF\xE0", 4) == 0) {
+	} else if (memcmp(picHeader, "\xFF\xD8\xFF", 3) == 0) {
 				isJPEG=true;
 				isPNG=false;
 	}

src/parsley.cpp

@@ -163,8 +163,7 @@ int APar_TestArtworkBinaryData(const char *artworkPath) {
     if (strncmp(twenty_byte_buffer, "\x89\x50\x4E\x47\x0D\x0A\x1A\x0A", 8) ==
         0) {
       artwork_dataType = AtomFlags_Data_PNGBinary;
-    } else if (strncmp(twenty_byte_buffer, "\xFF\xD8\xFF\xE0", 4) == 0 ||
-               memcmp(twenty_byte_buffer, "\xFF\xD8\xFF\xE1", 4) == 0) {
+    } else if (memcmp(twenty_byte_buffer, "\xFF\xD8\xFF", 3) == 0) {
       artwork_dataType = AtomFlags_Data_JPEGBinary;
     } else {
       fprintf(stdout,