Support paths containing spaces on Windows

Quote the arguments of "adb push" to support paths which contain spaces
on Windows.

Fixes <https://github.com/Genymobile/scrcpy/issues/288>.

app/src/str_util.c

@@ -1,5 +1,8 @@
 #include "str_util.h"
 
+#include <stdlib.h>
+#include <string.h>
+
 size_t xstrncpy(char *dest, const char *src, size_t n) {
     size_t i;
     for (i = 0; i < n - 1 && src[i] != '\0'; ++i)
@@ -31,3 +34,16 @@ truncated:
     dst[n - 1] = '\0';
     return n;
 }
+
+char *strquote(const char *src) {
+    size_t len = strlen(src);
+    char *quoted = malloc(len + 3);
+    if (!quoted) {
+        return NULL;
+    }
+    memcpy(&quoted[1], src, len);
+    quoted[0] = '"';
+    quoted[len + 1] = '"';
+    quoted[len + 2] = '\0';
+    return quoted;
+}