fix clang "always true" warning in lzma/main.cpp

outSize must be of type SizeT, because we pass its address to LzmaEncode or LzmaDecode.  How about this:

```
diff --git a/src/lzma/main.cpp b/src/lzma/main.cpp
index 247c8c6..a73c3e0 100644
--- a/src/lzma/main.cpp
+++ b/src/lzma/main.cpp
@@ -89,26 +89,23 @@ int main(int argc, const char** argv)
     const unsigned PropHeaderSize = 5;
     const unsigned HeaderSize = 13;
 
-    SizeT outSize;
+    int64_t outSize64;
     if (encode) {
-      outSize = size * 2;
+      outSize64 = size * 2;
     } else {
-      int32_t outSize32 = read4(data + PropHeaderSize);
-      if (outSize32 >= 0) {
-        outSize = outSize32;
-      } else if (argc == 5) {
-        outSize = atoi(argv[4]);
-      } else {
-        outSize = -1;
+      outSize64 = read4(data + PropHeaderSize);
+      if (outSize64 < 0 and argc == 5) {
+        outSize64 = atoi(argv[4]);
       }
     }
 
-    if (static_cast<int32_t>(outSize) >= 0) {
-      uint8_t* out = static_cast<uint8_t*>(malloc(outSize));
+    if (outSize64 >= 0) {
+      uint8_t* out = static_cast<uint8_t*>(malloc(outSize64));
       if (out) {
         SizeT inSize = size;
         ISzAlloc allocator = {myAllocate, myFree};
         ELzmaStatus status = LZMA_STATUS_NOT_SPECIFIED;
+        SizeT outSize = outSize64;
         int result;
         if (encode) {
           CLzmaEncProps props;
diff --git a/src/lzma/main.cpp b/src/lzma/main.cpp
index 247c8c6..a73c3e0 100644
--- a/src/lzma/main.cpp
+++ b/src/lzma/main.cpp
@@ -89,26 +89,23 @@ int main(int argc, const char** argv)
     const unsigned PropHeaderSize = 5;
     const unsigned HeaderSize = 13;
 
-    SizeT outSize;
+    int64_t outSize64;
     if (encode) {
-      outSize = size * 2;
+      outSize64 = size * 2;
     } else {
-      int32_t outSize32 = read4(data + PropHeaderSize);
-      if (outSize32 >= 0) {
-        outSize = outSize32;
-      } else if (argc == 5) {
-        outSize = atoi(argv[4]);
-      } else {
-        outSize = -1;
+      outSize64 = read4(data + PropHeaderSize);
+      if (outSize64 < 0 and argc == 5) {
+        outSize64 = atoi(argv[4]);
       }
     }
 
-    if (static_cast<int32_t>(outSize) >= 0) {
-      uint8_t* out = static_cast<uint8_t*>(malloc(outSize));
+    if (outSize64 >= 0) {
+      uint8_t* out = static_cast<uint8_t*>(malloc(outSize64));
       if (out) {
         SizeT inSize = size;
         ISzAlloc allocator = {myAllocate, myFree};
         ELzmaStatus status = LZMA_STATUS_NOT_SPECIFIED;
+        SizeT outSize = outSize64;
         int result;
         if (encode) {
           CLzmaEncProps props;
```